Book of abstracts, "Jaszowiec" 2011 - Instytut Fizyki PAN

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This work relates to Department of the Navy Grant N62909-11-1-1076 issued by Office of 

Naval Research Global. The United States Government has a royalty-free license throughout 

the world in all copyrightable material contained herein. 

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Skład własny (Ł. Cywi�ski, podzi�kowania dla T. Słupi�skiego) 

Druk i oprawa: Drukarnia Zalesie, 05-501 Piaseczno, ul. Norwida 10 

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PREFACE 

The 40 th “Jaszowiec” International School and Conference on the Physics of 

Semiconductors continues the tradition of annual meetings of the international and Polish 

semiconductor communities. For the third time the event will be held in the mountain resort 

Krynica-Zdrój on June 25 th – July 1 st , 2011. The first thirty seven meetings took place in the 

village Jaszowiec in another part of Polish mountains. For years, the name “Jaszowiec” has 

become the symbolic trademark of the conference and, therefore, it is still kept. 

The scope of the conference covers essentially all research fields in semiconductor 

physics, including technology, experiment, theory and modeling. During the present 

conference particular attention will be paid to the physics of semiconductor devices, and a 

special day-long symposium “Physics and modeling of devices” has been organized. 

The Conference is preceded by the School (tutorial session), addressed mainly to 

undergraduate and graduate students, and young scientists. The School will be held on June 

25 th -26 th . During the School outstanding scientists will give four lectures providing an 

introduction to important fields in semiconductor physics. The scientific program of the 

school and conference consists of 25 invited lectures, and 194 contributed papers (18 chosen 

for oral presentation and 176 posters). The School and Conference will be attended by 

approximately 250 participants. 

This booklet contains the detailed program and abstracts of all presentations that will 

be given during the event. The invited and contributed papers will be published in a special 

volume of Acta Physica Polonica A. 

The International School and Conference is organized by two institutes of the Polish 

Academy of Sciences: Institute of Physics and Institute of High Pressure Physics; two 

institutes of the Faculty of Physics, University of Warsaw: Institute of Experimental Physics 

and Institute of Theoretical Physics; Foundation “Pro Physica”, and Committee on Physics of 

the Polish Academy of Sciences. The financial support of the organizing institutions as well 

as of the U.S. Army Forward Element Command-Atlantic, Research Division (USARFEC-A) 

and the U.S. Navy Office of Naval Research Global is gratefully acknowledged. 

Current information can be found on the conference web page: 

www.ifpan.edu.pl/jaszowiec . 

I would like to thank the members of the International Advisory Committee and the 

Program Committee for their contribution to the scientific program of the School and 

Conference. I would like also to express my gratitude to Łukasz Cywi�ski, the Secretary of 

the Conference, to Jacek Szczytko, the Chairman of the School, as well as other members of 

the Organizing Committee, Agnieszka J�drzejewska and Maciek Zaj�czkowski for their 

enthusiasm and excellent work. 

I wish all the participants of the meeting scientifically inspiring days and joyful social 

life. Have a pleasant stay in Krynica. 

Chairman of the Conference 

Czesław Skierbiszewski

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors 

Saturday, June 25 th , 2011 

9:20 -- 9:30 Jacek Szczytko – School opening address 

INVITED LECTURES (SaI1, SaI2) 

9:30 – 12:30 Detlef Hommel (University of Bremen, Germany) 

Modern technologies for semiconductor epitaxy and nano-processing 

15:00 – 18:00 Aldo Di Carlo (University of Rome “Tor Vergata”, Italy) 

Physical simulation of electronic devices 

19:00 Barbecue (on the terrace of the ‘Geovita’ hotel) 

Sunday, June 26 th , 2011 

INVITED LECTURES (SuI1, SuI2) 

9:30 – 12:30 Gerhard Abstreiter (Walter Schottky Institut and Institute for Advanced 

Study TU München, Germany) 

Physics and Technology of Arsenide Based Quantum Dots and Nanowires 

15:00 – 18:00 Debdeep Jena (University of Notre Dame, USA) 

Tutorial: Engineering of Electric Fields in Nitride-Based Semiconductors 

20:30 – 21:30 Concert – chamber music performed by young artists, 

laureates of international music competitions 

Angelika Kumi�ga (violin) 

Agata B�k (cello) 

Michał Kubarski (accordion) 

21:30 Welcoming glass of wine 

5

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40th "Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors 

Monday, June 27 th , 2011 

8:50 -- 9:00 Czesław Skierbiszewski – Conference opening address 

INVITED TALKS (MoI1 … MoI4) 

9:00 – 10:00 Joerg Wrachtrup (University of Stuttgart, Germany) 

Coherent optical control of the NV center in diamond 

10:00 – 10:10 Break 

10:10 – 11:10 Tomasz Dietl (Institute of Physics, Polish Academy of Sciences) 

Understanding and exploiting magnetism of semiconductors 

11:10 – 11:40 Coffee break 

11:40 – 12:40 Łukasz Kłopotowski (Institute of Physics, Polish Academy of Sciences) 

Charging Effects in Self Assembled CdTe Quantum Dots 

12:40 – 12:50 Break 

12:50 – 13:50 Grzegorz S�k (Wrocław University of Technology, Poland) 

Optical properties of strongly in-plane asymmetric epitaxial 

nanostructures 

CONTRIBUTED TALKS (MoO1 … MoO6) 

19:15 – 19:30 P. Utko, R. Ferone, I.V. Krive, R.I. Shekhter, M. Jonson, M. Monthioux, 

L. Noe, J. Nygård 

Coupling between electronic and vibrational excitations in carbon 

nanotubes filled with C60 fullerenes 

19:30 – 19:45 A. Urba�czyk, F.W M. van Otten, R. Nötzel 

Solid-state self assembly: a route to hybrid metal-semiconductor epitaxial 


19:45 – 20:00 M. Galicka, P. Kacman, R. Buczko 

First-Principles Study of Doped III–V nanowires 

20:00 – 20:10 Break 

20:10 – 20:25 F. Schuster, P. Kopyt, P. Lukasik, W. Gwarek, D. Coquillat, F. Teppe, 

B. Giffard, W. Knap 

Terahertz Detectors Based on Low Cost 130 nm Silicon Field Effect 

Transistors 

20:25 – 20:40 P. Wojnar, E. Janik, S. Kret, A. Petrouchik, M. Goryca, T. Kazimierczuk, 

P. Kossacki, G. Karczewski, T. Wojtowicz 

Growth of optically active CdTe quantum dots in ZnTe nanowires 

20:40 – 20:55 J.M. Schneider, B.A. Piot, I. Sheikin, G.A. Goncharuk, P. Vasek, 

P. Svoboda, Z. Vyborny, L. Smrcka, M. Orlita, M. Potemski, D.K. Maude 

Electronic properties of graphite 

21:05 – 23:00 MONDAY POSTER SESSION (MoP1 … MoP60) 

6

40th _______________________________________________________________ 


Tuesday, June 28 th , 2011 

INVITED TALKS (TuI1 … TuI4) 

9:00 – 10:00��Alex Greilich��(Technische Universität Dortmund, Germany) 

Optical control of one and two spins in interacting quantum dots 

10:00 – 10:10 Break 

10:10 – 11:10 Shaffique Adam (National Institute of Standards and Technology, USA) 

Graphene Transport Properties 

11:10 – 11:40 Coffee Break 

11:40 – 12:40 Arkadiusz Wójs (Wrocław University of Technology, Poland) 

Theoretical search for non-Abelian statistics in fractional quantum Hall 

states 

12:40 – 12:50 Break 

12:50 – 13:50 Dmitry Krizhanovskii (University of Sheffield, UK) 

Polariton condensation in dynamic acoustic lattices 

CONTRIBUTED TALKS (TuO1 … TuO6) 

15:30 – 15:45 K. Nogajewski, K. Karpierz, M. Grynberg, W. Knap, R. Gaska, J. Yang, 

M.S. Shur, J. Łusakowski 

Resonant Terahertz Absorption by Magnetoplasmons in Grating-Gate 

GaN/AlGaN-based Field-Effect Transistors 

15:45 – 16:00 K. Milowska, M. Birowska, J.A. Majewski 

Structural and electronic properties of functionalized graphene 

16:00 – 16:15 O. Proselkov, W. Stefanowicz, S. Dobkowska, J. Sadowski, T. Dietl, 

M. Sawicki 

Analysis of the magnetic anisotropy in ultrathin GaMnAs 

16:15 – 16:25 Break 

16:25 – 16:40 M. Goryca, P. Plochocka, P. Wojnar, T. Kazimierczuk, M. Potemski, 

P. Kossacki 

Spin-lattice relaxation of a single Mn 2+ ion in a CdTe quantum dot 

16:40 – 16:55 T. Kazimierczuk, M. Goryca, P. Wojnar, A. Golnik, P. Kossacki 

Magnetophotoluminescence of CdTe/ZnTe Quantum Dots: G-factor and 

Diamagnetic Shift Variation in a Single Dot 

16:55 – 17:10 T. Jakubczyk, W. Pacuski, A. Golnik, C. Kruse, D. Hommel, H. Hilmer, 

R. Schmidt-Grund, J.A. Gaj 

Control over CdTe Quantum Dots Emission using ZnTe-based Micropillar 

Cavities 

17:30 – 19:15 TUESDAY POSTER SESSION (TuP1 … TuP58) 

20:00 Conference Banquet 

7

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Wednesday, June 29 th , 2011 

INVITED TALKS (WeI1 … WeI4) 

9:00 – 10:00 Tomas Jungwirth (Institute of Physics, Academy of Sciences of the Czech 

Republic) 

Spintronics with antiferromagnetic materials 

10:00 – 10:10 Break 

10:10 – 11:10 Ewelina M. Hankiewicz (Universitaet Wuerzburg, Germany) 

Transport in topological insulators 

11:10 – 11:40 Coffee Break 

11:40 – 12:40 James Speck (University of California, Santa Barbara) 

Progress in Nonpolar and Semipolar GaN Materials and Devices 

12:40 – 12:50 Break 

12:50 – 13:50 Yasushi Nanishi (Ritsumeikan University, Japan, and Seoul National 

University, Korea) 

Recent Progress of DERI process for growth of InN and Related Alloys 

CONTRIBUTED TALKS (WeO1 … WeO6) 

19:15 – 19:30 N. Gonzalez Szwacki, J. A. Majewski, T. Dietl 

Properties of TM pairs in the bulk and at the surface of GaN with and 

without Si or Mg codoping 

19:30 – 19:45 A. Bonanni, W. Stefanowicz, M. Sawicki, T. Devillers, B. Faina, T. Li, 

T.E. Winkler, D. Sztenkiel, A. Navarro-Quezada, M. Rovezzi, R. Jakieła, 

A. Meingast, G. Kothleitner, T. Dietl 

Experimental Probing of Exchange Interactions Between Localized Spins 

in a Dilute Magnetic Insulator (Ga,Mn)N 

19:45 – 20:00 M. Birowska, C. �liwa, K. Milowska, J.A. Majewski, T. Dietl 

Origin of uniaxial magnetic anisotropy in (Ga,Mn)As 

20:00 – 20:10 Break 

20:10 – 20:25 E. Calleja, A. Bengoechea-Encabo, S. Albert, M.A. Sanchez-García, 

F. Barbagini, E. Luna, A. Trampert, U. Jahn, P. Lefebvre 

Understanding the Selective Area Nucleation and Growth of GaN 

20:25 – 21:40 S.P. Łepkowski, I. Gorczyca 

Influence of composition and atomic arrangement on elastic properties of 

wurtzite InGaN and InAlN alloys 

20:40 – 20:55 H. Turski, M. Siekacz, M. Sawicka, G. Cywi�ski, C. Cheze, S. Grzanka, 

Z. Wasilewski, P. Perlin, G. Muzioł, J. Pawłowska, I. Grzegory, 

C. Skierbiszewski 

InGaN laser diodes operating at 450-460 nm grown by RF-Plasma MBE 

21:05 – 23:00 WEDNESDAY POSTER SESSION (WeP1 … WeP58) 

8

40th _______________________________________________________________ 


Thursday, June 30 th , 2010 

SYMPOSIUM 

"Physics and modeling of devices " 

INVITED TALKS (ThI1 …ThI9) 

9:00 – 9:30 Maciej Bugajski (Institute of Elektron Technology, Warsaw, Poland) 

Quantum Cascade Lasers 

9:30 – 10:00 Wladek Walukiewicz (Lawrence Berkeley National Laboratory,USA) 

New Concepts and Materials for Solar Power Conversion Devices 

10:00 – 10:10 Break 

10:10 – 10:40 Danek Elbaum (Institute of Physics, Polish Academy of Sciences) 

ZnO biosensing 

10:40 – 11:10 Katarzyna Holc (Institute of High Pressure Physics, Warsaw, Poland) 

Nitride laser diodes 

11:10 – 11:30 Coffee break 

11:30 – 12:00 Detlef Hommel (University of Bremen, Germany) 

Application of CdSe quantum dots for single photon emitters at room 

temperature 

12:00 – 12:30 Wojciech Knap (University of Montpellier, France) 

THz emitters based on GaN/AlGaN HEMTs 

12:30 -- 13:00 Tomasz Stobiecki (AGH University of Science and Technology, Kraków, 

Poland) 

Spin transfer torque in TMR and GMR nanostructures for spintronic 

devices 

15:00 – 15:30 Jan Dziuban (Wrocław University of Technology, Poland) 

Si-based MEMS devices 

15:30 – 16:00 Zbigniew Ku�nicki (Ecole Nationale Superiere de Physique, Illkirch- 

Graffenstaden) 

Giant photoconversion on silicon drived materials 

16:00 Czesław Skierbiszewski – Closing address 

19:00 Farewell dinner 

9

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MONDAY POSTER SESSION (MoP1 …MoP60) 

1. K.A. Kolwas, G. Grabecki, S. Trushkin, Ł. Cywi�ski, M. Aleszkiewicz, T. Dietl, G. 

Springholz, G. Bauer 

Nonlocal transport in PbTe/PbEuTe microstructures 

2. M. Szot, L. Kowalczyk, E. Smajek, B. Taliashvili, P. Dziawa, W. Knoff, A. Reszka, V. 

Domukhovski, E. Łusakowska, P. Dłu�ewski, M. Wiater, T. Wojtowicz, T. Story, M. 

Bukała, R. Buczko, P. Kacman 

Optical transitions in PbTe/CdTe quantum wells grown by molecular beam epitaxy on 

GaAs (001) and BaF2 (111) substrates 

3. A. Woło�, A. Drabinska, M. Kaminska, G. Strzelecka, A. Hruban, A. Materna, M. Piersa, 

Z. Wilamowski 

Properties of three-dimensional topological insulators studied by microwave resonance 

spectroscopy 

4. A. Duzynska, A. Kaminska, H. Teisseyre, E. Przezdziecka, D. Dobosz, Z.R. Zytkiewicz, 

A. Kozanecki, J.D. Fidelus, A. Durygin, V. Drozd, R. Hrubiak, A. Suchocki 

Analysis of Optical Properties and Pressure Dependence of the Energy Gap of ZnO 

Layers, Bulk and Nano-Powders 

5. A. Radzvilavicius, E. Anisimovas 

Defect structure of two-dimensional Wigner crystals 

6. A. Korbecka, J.A. Majewski 

Gauge invariant computational scheme for heterostructures in magnetic field 

7. M. Bukała, P. Sankowski, R. Buczko, P. Kacman 

Modeling PbTe-based low dimensional structures 

8. A. Hruban, A. Materna, W. Dalecki, G. Strzelecka, M. Piersa, E. Jurkiewicz-Wegner, R. 

Diduszko, M. Romaniec, W. Orłowski 

Topological insulators – materials for fundamental researches and perspective 

applications 

9. M. Chwastyk, P.T. Ró�a�ski, M. Zieli�ski 

Atomistic calculation of screened Coulomb interactions in semiconductor 


10. M. Birowska, K. Milowska, J.A. Majewski 

Van der Waals Density Functionals in Materials Science 

11. T. Gro�, E. Malicka, A.W. Pacyna, H. Duda, J. Krok-Kowalski 

Hopkinson-Like Effect in Single-Crystalline CdCr2Se4 Semiconductor 

12. Ł. Wachnicki, B.S. Witkowski, S. Gierałtowska, E. Janik, M. Godlewski, E. Guziewicz 

Optical and structural characterization of zinc oxide nanostructures obtained by 

Atomic Layer Deposition method 

10

40th _______________________________________________________________ 


13. V.V. Khomyak, M.I. Ilaschuk, O.A. Parfenyuk, V.V. Brus, Z.D. Kovalyuk 

Electrical properties of surface-barrier structures n-Zn1-xCdxO/ p-CdTe 

14. E.A. Wolska, D. Sibera, B.S. Witkowski, S.A. Yatsunenko, I. Pełech, U. Narkiewicz, M. 

Godlewski 

Photoluminescence and chromaticity properties of ZnO nanopowders obtained by a 

microwave solwothermal method 

15. T. Š�epka, D. Gregušová, R. Kúdela, Š. Gaži, V. Cambel 

Technology and testing the mechanical properties of the InGaP/GaAs/InGaP 

microcantilevers 

16. M.A. Borysiewicz, E. Dynowska, V. Kolkovsky, J. Dyczewski, E. Kami�ska, A. 

Piotrowska 

ZnO thin films of different crystalline structures grown on Si (100) substrates by 

reactive DC sputter deposition 

17. W. Knoff, M.A. Pietrzyk, B.A. Orłowski, B. Taliashvili, T. Story, R.L. Johnson 

Comparison of the valence band of amorphous and crystalline GeTe and (Ge,Mn)Te 

layers 

18. A. Pietnoczka, R. Bacewicz, T. Słupi�ski, S.H. Wei, M. Jie, J. Antonowicz, T. Drobiazg 

Local Structure Study of GaAs:Te Using Te K-edge X-ray Absorption Fine Structure 

19. A. Taube, K. Korwin-Mikke, R. Mroczy�ski, S. Gierałtowska, A. Łaszcz, I. Pasternak, 

M. Sochacki, M. Zychowska, J. Dyczewski, M. Zdrojek, E. Dynowska, A. Piotrowska 

Thermal Stability of HfO2/SiO2 Gate Stack on Silicon Substrate 

20. M. Iwi�ska, D. Pier�ci�ska, K. Pier�ci�ski, A. Szerling, P. Karbownik, M. Bugajski 

Investigation of thermal properties of AlGaAs/GaAs Quantum Cascade Lasers by 

thermoreflectance spectroscopy 

21. P. Łach, M.G. Brik, I. Sildos, A. Kami�ska, A. Suchocki 

Luminescence properties of Sm 3+ in different phases of TiO2 

22. L.A. Karachevtseva, S.Ya. Kuchmii, O.A. Lytvynenko, F.F. Sizov, O.J. Stronska, A.L. 

Stroyuk 

Investigation of electro-optical properties of 2D macroporous silicon 

23. G.V. Lashkarev, A.M. Yaremko, V.A. Karpyna 

Investigation of multi-phonon excitations in ZnO textured crystalline films by Raman 

spectroscopy 

24. M.L. Peres, V.A. Chitta, D.K. Maude, N.F. Oliveira Jr., P.H. Rappl, A.Y. Ueta, E. 

Abramof 

Rashba effect in n-type PbTe/Pb1-xEuxTe Quantum Wells 

11

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25. I.I. Shtepliuk, G.V. Lashkarev, O.Yu. Khyzhun, V.V. Khomyak, V.I. Lazorenko, I.I. 

Timofeeva, L.A. Klochkov, B. Kowalski, A. Reszka 

Enhancement the intensity of ultraviolet luminescence of ZnO film upon doping 

isovalent impurity of cadmium 

26. V.V. Brus, Z.D. Kovalyuk, P.D. Maryanchuk 

Optical Properties of TiO2 – MnO2 Thin Films Prepared by the Electron-Beam 

Evaporation Technique 

27. S. Gierałtowska, Ł. Wachnicki, B.S. Witkowski, T.A. Krajewski, M. Godlewski, E. 

Guziewicz 

Properties of high-k oxides grown by Atomic Layer Deposition method for transparent 

electronics 

28. E. Maci��ek, T. Gro�, A.W. Pacyna, T. Mydlarz, J. Krok-Kowalski 

High Spin-Low Spin Transitions in Cu0.2Co0.76Cr1.83Se4 Semiconductor 

29. D. Shevchenko, J. Mickevi�ius, G. Tamulaitis, N. Starzhinskiy, K. Katrunov, V. 

Ryzhikov 

Photoluminescence Study of ZnSe Scintillating Crystals Doped with Isovalent 

Tellurium and Oxygen 

30. K. Olender, T. Wosi�ski, A. M�kosa, P. Dłu�ewski, V. Kolkovsky, G. Karczewski 

Native Deep-Level Defects in MBE-Grown p-Type CdTe 

31. P. Urbanowicz, E. Tomaszewicz, T. Gro�, H. Duda, Z. Kukuła 

Residual Paramagnetism at High-Temperature CuEu2W2O10 and Cu3Eu2W4O18 

Semiconductors 

32. M.V. Radchenko, G.V. Lashakrev, M.E. Bugaiova, V.I. Sichkovskyi, V.I. Lazorenko, 

L.A. Krushynskaya, Y.A. Stelmakh, W. Knoff, T. Story 

Ferromagnetic nanocomposite Co-Al2O3 as a spintronic material with engineered 

magnetic properties 

33. D.M. Bercha, K.E. Glukhov, M. Sznajder, S.A. Bercha 

The role of electron subsystem in the phase transition process in a layered CuInP2S6 

crystal 

34. A..I. Dmitriev 

Van der Waals surface of InSe as a standard nanorelief in the metrology of 

nanoobjects 

35. A. Kaminska, C.G. Ma, M.G. Brik, A. Kozanecki, M. Bo�kowski, E. Alves, A. Suchocki 

Crystal field analysis of the Yb 3+ energy level scheme in III-V semiconductors 

36. J. Weszka, M. Doma�ski, J. Jurusik, B. Hajduk, M. Chwastek, H. Bednarski 

Studies of Electric Transport Properties of Single Layer Devices Based on the 

Polyazomethine Thin Films 

12

40th _______________________________________________________________ 


37. R. Jarimavi�iu-te.-Žvalioniene., I. Prosy�evas, Ž. Kaminskiene., S. Lapinskas 

Optical properties of black silicon with precipitated silver and gold nanoparticles 

38. I.P. Koziarskyi, P.D. Marianchuk, E.V. Maistruk, D.P. Koziarskyi 

Optical Properties of Crystals (3HgSe)0.5(In2Se3)0.5, (3HgS)0.5(In2S3)0.5, 

(3HgS)0.5(Al2S3)0.5, (3HgSe)0.5(Al2Se3)0.5, Doped with Mn or Fe 

39. N.S. Yurtsenyuk 

Self-Compensation Mechanism in Semi-Insulating CdMnTe:Sn Crystals Intended for 

X/�-Ray Detectors 

40. J. Krok-Kowalski, G. Władarz, T. Gro�, H. Duda, A.W. Pacyna, K. Nikiforov, P. Rduch 

Influence of Cu, Ga and Au Dopants and Technology Conditions on the Magnetic 

Interactions in HgCr2Se4 Single Crystals 

41. A.I. Ievtushenko, G.V. Lashkarev, V.I. Lazorenko, Z.J. Horvath, M.G. Dusheyko 

The Photodetectors with Vertical Integration Based on ZnO Films 

42. A.I. Ievtushenko, G.V. Lashkarev, V.I. Lazorenko, O.Y. Khyzhun, L.O. Klochkov, O.I. 

Bykov, V.M. Tkach, V.A. Baturin, A.Y. Karpenko 

Features of the Properties for Nitrogen Doping and Al-N Codoping of ZnO Films 

43. A.I. Ievtushenko, G.V. Lashkarev, V.I. Lazorenko, L.O. Klochkov, O.I. Bykov, O.M. 

Kutsay, S.P. Starik, V.A. Baturin, A.Y. Karpenko 

Influence of Oxygen Pressure on the Properties of AZO Films 

44. H. Duda, E. Malicka, T. Gro�, A. G�gor, R. Sitko, J. Krok-Kowalski, P. Rduch 

Thermoelectric Power of CuCrxVySe4 p-Type Spinel Semiconductors 

45. H. Duda, P. Rduch, E. Malicka, T. Gro�, A. G�gor 

Critical Behaviour of the 3D-Heisenberg Ferromagnetic 

46. J.M. Sajkowski, M.A. Pietrzyk, D. Dobosz, M. Stachowicz, A. Droba, E. Przezdziecka, 

A. Wierzbicka, A. Kozanecki 

Optical properties of ZnO/ZnMgO single quantum wells grown by molecular beam 

epitaxy 

47. B.A. Orłowski, S.P. Dziawa, A. Reszka, K. Gas, S. Mickievicius, S. Thiess, W. Drube 

Electronic structure of CdTe/PbEuTe/CdTe 

48. D. Ziółkowska, K.P. Korona, M. Kami�ska, S.H. Wu, M.S. Chen 

Raman Spectroscopy of LiFePO4 and Li3V2(PO4)3 Cathode Materials for Lithium-Ion 

Battery Applications 

49. M. Hosatte, M.Ł. Basta, B.S. Witkowski, Z.T. Ku�nicki, M. Godlewski 

Multi-interface layered P-doped silicon structures for third generation photovoltaics 

50. M. Stachowicz, E. Przezdziecka, D. Dobosz, M.A. Pietrzyk, J.M. Sajkowski, A. Droba, 

A. Wierzbicka, A. Kozanecki 

Optical Properties of Thin ZnO Layers Grown by MBE 

13

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51. K. Gas, E. Dynowska, E. Janik, A. Kami�ska, S. Kret, J.F. Morhange, I. Pasternak, M. 

Wiater, W. Zaleszczyk, R. Hołyst, E. Kami�ska, T. Wojtowicz, W. Szuszkiewicz 

ZnO-based Nanotubes Obtained by the Oxidation of ZnTe and ZnTe/Zn Nanowires 

52. D. �ak, W. Nakwaski 

Composition-dependent thermal resistance of multilayered structures taking into 

account phonon reflection, scattering and tunneling 

53. A. Reszka, B.A. Orłowski, M.A. Pietrzyk, A. Szczerbakow, S. Mickievicius, S. 

Balakauskas, R.L. Johnson 

Pb1-xGexTe surface with Sm 2+ and Sm 3+ doping 

54. H. Bednarski, J. Weszka, M. Doma�ski, V. Cozan 

Studies of Optical Properties of Protonated Poliazomethine Thin Films 

55. A.V. Atrashchenko, V.P. Ulin, V.P. Evtikhiev 

The reasons of destruction of nanoporous GaAs matrix fabricated by electrochemical 

etching 

56. E. Malicka, T. Gro�, A.W. Pacyna, H. Duda, J. Krok-Kowalski 

Effect of Substitution of Ti for Cd in CdCr2Se4 p-Type Semiconductor 

57. K. Dybko , M. Szot, T. Story, G. Karczewski, S. Schreyeck, C. Schumacher, K. Brunner 

and L. W. Molenkamp 

Thermoelectric power in epitaxial Bi2Se3/Si(111) layers 

58. M. Zapalska and T. Doma�ski 

Diamagnetism of the pre-paired electronic systems: the flow equation study 

59. N. Gonzalez-Szwacki, J.A. Majewski 

Quantum Monte Carlo vs. Density Functional Methods for the prediction of relative 

energies of small Si-C clusters 

60. M. Koba and P. Szczepa�ski 

Analysis of a Spatial Hole Burning Effect in a Square and Triangular Lattice Photonic 

Crystal Laser 

14

40th _______________________________________________________________ 


TUESDAY POSTER SESSION (TuP1 …TuP58) 

1. T. Smole�ski, Ł. Cywi�ski, M. Goryca, P. Kossacki 

Exciton and Mn spin dynamics in a nonresonantly coupled pair of (Cd,Mn)Te 

quantum dots 

2. J. Kobak, W. Pacuski, T. Kazimierczuk, J. Suffczy�ski, T. Jakubczyk, A. Golnik, 

P. Kossacki, M. Nawrocki, J.A. Gaj, C. Kruse, D. Hommel 

Three-dimensional anisotropy studies of CdTe quantum dots 

3. K. Grodecki, W. Strupi�ski, A. Wysmołek, R. St�pniewski, J.M. Baranowski 

Probing electron concentration in epitaxial graphene using Raman spectroscopy 

4. M. Zieli�ski, G.W. Bryant, N. Malkova, J. Sims, W. Jaskolski, J. Aizpurua 

Dynamical control of excitonic fine structure with nanomechanical strain 

5. K. Roszak, T. Novotný 

Non-Markovian noise at the Fermi-edge singularity in quantum dots 

6. M. Czapkiewicz, J. Wróbel, V. Kolkovsky, P. Nowicki, M. Aleszkiewicz, M. Wiater, 

T. Wojtowicz 

Transport and Spin Properties of CdTe/CdMgTe Quantum Point Contacts 

7. M. Kozub, P. Machnikowski 

The Role of Strong Coupling in the Superradiance of Ensembles of Quantum Dots 

8. M. Szymura, Ł. Kłopotowski, P. Wojnar, K. Fronc, T. Kazimierczuk, G. Karczewski, 

T. Wojtowicz 

Photoluminescence Linewidth Analysis of Single CdMnTe Quantum Dots 

9. M. Koperski, T. Kazimierczuk, M. Goryca, A. Golnik, J.A. Gaj, M. Nawrocki, 

P. Wojnar, P. Kossacki 

Statistical Study of the Inter-Dot Excitation Transfer in CdTe/ZnTe Quantum Dots. 

10. Ł. Marcinowski, M. Krzy�osiak, K. Roszak, P. Machnikowski, R. Buczko, J. Mostowski 

Phonon influence on the weak measurement of double quantum dot spin states. 

11. P. Kaczmarkiewicz, A. Musiał, G. S�k, P. Podemski, J. Misiewicz, P. Machnikowski 

Influence of Carrier Trapping on the Optical Properties of InAs/InP Quantum Dashes 

12. K. Dziatkowski, D. Ratchford, T. Hartsfield, X. Li, Y. Gao, Z. Tang 

CdSe/ZnS Colloidal Quantum Dots with Alloyed Core/Shell Interfaces: 

a Photoluminescence Dynamics Study 

13. K. Kukli�ski, Ł. Kłopotowski, K. Fronc, P. Wojnar, T. Wojciechowski, M. Czapkiewicz, 

J. Kossut, G. Karczewski, T. Wojtowicz 

Spectroscopy of Indirect Excitons in Vertically Stacked CdTe Quantum Dot Structures 

15

_______________________________________________________________ 


14. W. Abdussalam, A. Sitek, P. Machnikowski 

Collective spontaneous emission from pairs of quantum dots: the role of coupling and 

system geometry 

15. K. Korzekwa, P. Machnikowski 

Tunneling transfer protocol in a quantum dots chain immune to inhomogeneity 

16. A. Musial, G. Sek, A. Marynski, P. Podemski, J. Andrzejewski, J. Misiewicz, A. Loeffler, 

S. Hoefling, S. Reitzenstein, J.P. Reithmaier, A. Forchel 

Thermal Quenching of Photoluminescence from epitaxial InGaAs/GaAs Quantum 

Dots with High Lateral Aspect Ratio 

17. P. Schillak, G. Czajkowski 

Excitonic Magnetoabsorption of Cylindrical Quantum Disks 

18. P. Karwat, A. Sitek, P. Machnikowski 

Spontaneous emission from double quantum dots: collective effects and carrier- 

phonon kinetics 

19. P. Łach, A. Reszka, G. Karczewski, P. Wojnar, T. Wojtowicz, A. Kami�ska, A. Suchocki 

Cathodoluminescence studies of the II – VI semiconducting quantum dots grown by 

molecular beam epitaxy 

20. E. Zielony, E. Popko, Z. Gumienny, P. Kamyczek, A. Henrykowski, J. Jacak, G. 

Karczewski 

Raman spectroscopy of CdTe/ZnTe quantum dots 

21. J. Bara�ski, T. Doma�ski 

Quantum interference in charge transport via the quantum dots coupled between 

the metallic and superconducting leads 

22. H. Bednarski, J. Spałek 

Bound magnetic polaron molecule in diluted magnetic semiconductors within the 

Heitler-London approximation 

23. M. Zału�ny, A. Kozłowski 

Intersubband polaritons in strongly pumped microcavities 

24. M.S. Mukhin, Y.V. Terent'ev, L.E. Golub, M.O. Nestoklon, B.Y. Meltser, 

A.N. Semenov, V.A. Solov'ev, A.A. Sitnikova, A.A. Toropov, S.V. Ivanov 

Magneto-Optical Studies of Narrow Band-Gap Heterostructures with Type II Quantum 

Dots InSb in an InAs Matrix 

25. K.H. Gawarecki, P. Machnikowski 

Phonon-assisted tunneling between hole states in double quantum dots 

26. I. Bragar, K. Gawarecki, P. Machnikowski 

Intermediate band formation for electrons and holes in an inhomogeneous chain of 

quantum dots 

16

40th _______________________________________________________________ 


27. O. Rancova, E. Anisimovas 

Modelling of 1D-2D structural transitions in small Yukawa clusters 

28. P. Kowalski, P. Machnikowski 

Efficient Coulomb mixing between single- and biexciton states in InAs nanocrystals 

29. K. Gołasa, M. Molas, J. Borysiuk, Z.R. Wasilewski, A. Babi�ski 

Strongly disordered wetting layer in the InAs/GaAs self-assembled quantum dots 

system 

30. M. Molas, K. Gołasa, J. Łusakowski, T. Wojtowicz, A. Babi�ski 

Optical transformation of zero-dimensional confinement in the CdTe/CdMgTe multiple 

quantum wells 

31. M. Kozub, A. Musiał, G. S�k, J. Misiewicz, V. Zürbig, J.P. Reithmaier 

Optical Properties of InGaAs Quantum Dots on (100) GaAs Substrates Formed by 

Droplet Epitaxy 

32. M. Molas, K. Gołasa, T. Kazimierczuk, J. Łusakowski, T. Wojtowicz, A. Babi�ski 

Magnetooptical study of excitons confined in potential fluctuations in the 

CdTe/CdMgTe quantum well 

33. A. Ballester, J.M. Escartín, J.L. Movilla, M. Pi, J. Planelles 

Mixed Correlation Phases In Elongated Quantum Dots 

34. J. Ebeling, T. Aschenbrenner, S. Figge, D. Hommel 

Simulation and Realization of Photonic Crystals in Light Emitting Devices 

35. E. Zielony, E. Popko, Z. Gumienny, G. Karczewski 

Electro-optical characterization of Ti/Au-ZnTe Schottky diodes with CdTe quantum 

dots 

36. J. Jadczak, L. Bryja, A. Wójs, G. Bartsch, D.R. Yakovlev, M. Bayer, M. Potemski 

Magneto-photoluminescence studies of many body scattering processes in two- 

dimensional hole gas 

37. H. Videlier, N. Dyakonova, F. Teppe, C. Consejo, W. Knap, J. Lusakowski, 

D. Tomaszewski, J. Marczewski, P. Grabiec 

Spin related effect in Si-MOSFETs THz Photoresponse 

38. N. Dyakonova, A. ElFatimy, Y. Meziani, D. Coquillat, W. Knap, F. Teppe, P. Buzatu, 

L. Varani, H. Marinchio, J. Torres, P. Nouvel 

THz emission related to hot plasmons and plasma wave instability in field effect 

transistors 

39. M. Białek, M. Czapkiewicz, K. Fronc, J. Wróbel, V. Umansky, M. Grynberg, 

J. Łusakowski 

A Comb-Like Shape of the Cyclotron Resonance Line in GaAs/AlGaAs 

Heterostructure 

17

_______________________________________________________________ 


40. J. Przybytek, M. Gryglas-Borysiewicz, M. Baj 

Impurity-Related Noise in Si �-doped Single-Barrier GaAs/AlAs/GaAs Resonant 

Tunneling Devices 

41. F. Teppe, C. Consejo, J. Torres, B. Chenaud, P. Solignac, Z.R. Wasilewski, M. Zholudev, 

N. Dyakonova, D. Coquillat, A. El Fatimy, W. Knap 

Current Driven Terahertz Detection of Quantum Cascade Laser Emission by Plasma 

Waves in Nano-Transistors 

42. G. K�pisty, K. Grodecki, W. Strupi�ski, A. Wysmołek, R. St�pniewski, J.M. Baranowski 

Influence of SiC substrate orientation on epitaxial graphene quality studied by Raman 

spectroscopy 

43. M. Syperek, B. Bujko, J. Jadczak, M. Kubisa, L. Bryja, J. Misiewicz 

Fermi edge and band-to-band recombination dynamics in n-doped GaAs/AlGaAs 

quantum well 

44. M. Kozubal, M. Gryglas-Borysiewicz, J. Przybytek, J. Borysiuk, M. Baj, R. St�pniewski, 

A. Wysmołek, W. Strupi�ski, J. Baranowski 

Magnetotransport Studies of Graphene Exposed to Water Vapours 

45. K. Grodecki, J.A. Błaszczyk, A. Dominiak, W. Strupi�ski, A. Wysmołek, 

R. St�pniewski, A. Drabi�ska, M. Sochacki, J.M. Baranowski 

Interaction of epitaxial graphene with SiC substrates studied by Raman spectroscopy 

46. K. Nogajewski, H. Boukari, P. Kopyt, W. Gwarek, T. Wojtowicz, H. Mariette, 

M. Grynberg, J. Łusakowski 

Antenna-Equipped Field Effect Transistors on CdTe/CdMgTe Quantum Wells as 

Terahertz Detectors 

47. A.D. Chegodaev, D.K. Loginov 

Effect of homogeneous electric field on exciton dispersion in wide quantum well 

48. V.Ya. Roshko 

Theoretical Analysis of Optical Losses in CdS/CdTe Solar Cells 

49. M.Kubisa, K.Ryczko and J.Misiewicz 

Anisotropy of B=0 spin splitting of holes in symmetric GaAs/Ga(1-x)AlxAs quantum 

wells 

50. J. Szczytko, P. Arcade, E. Papis, A. Bara�ska, B. Pi�tka, J. Łusakowski 

Terahertz Properties of Gold Layers on GaAs 

51. P. Sznajder, B. Pi�tka, J. Szczytko, J. Łusakowski 

Towards Optically Tunable Terahertz Plasmonic Detectors 

52. I. Grigelionis, K. Fobelets, B. Vincent, J. Mitard, B. DeJaeger, E. Simoen, D. Jaworski, 

J. Łusakowski 

Mobility of Holes in Nanometer Ge-on-Si p-type Metal-Oxide-Semiconductor Field- 

Effect Transistors at Low Temperatures 

18

40th _______________________________________________________________ 


53. Paweł Utko, Morten H. Madsen, Trine Berthing, Sara Bonde, Claus B. Sorensen, 

Karen L. Martinez, Jesper Nygard 

Vertical InAs nanowires as biological probes 

54. M. �ciesiek, T. Jakubczyk, W. Pacuski, A. Golnik, P. Kossacki, C. Kruse, D. Hommel 

Towards better light-confinement in pillar cavities 

55. M. Rawski, J. �uk, A. Drozdziel, K. Pyszniak, M. Turek 

Investigation of ion-implanted SiC properties by means of a light absorption technique 

56. P. Kamyczek, E. Placzek-Popko, Łukasz Gelczuk, Maria D�browska-Szata 

SiC Schottky barrier diode studied by admittance spectroscopy 

57. P. Sitarek, K. Ryczko, J. Misiewicz, D. Reuter, A. Wieck 

Optical transitions between confined and unconfined states in p-type asymmetric 

GaAs/InGaAs/AlGaAs QW structures 

58. K. Tahy, W. S. Hwang, J.L. Tedesco, R.L. Myers Ward, P.M. Campbell, C.R. Eddy Jr., 

D.K. Gaskill, H. Xing, A. Seabaugh, D. Jena 

Sub-10 nm Epitaxial Graphene Nanoribbon FETs 

19

_______________________________________________________________ 


WEDNESDAY POSTER SESSION (WeP1 …WeP58) 

1. C. �liwa, T. Dietl 

Thermodynamic and thermoelectric properties of (Ga,Mn)As 

2. M. Sobanska, K. Klosek, Z.R. Zytkiewicz, J. Borysiuk, A. Wierzbicka, A. Reszka, E. 

Lusakowska 

Plasma-assisted molecular beam epitaxy of GaN on Si (111) substrates 

3. J. Plaziak, J. Higersberger, J.A. Majewski 

Role of Interface Carrier Transport in Electrical Characteristics of Light Emitting 

Devices Based on Heterostructures 

4. A. Łusakowski, P. Bogusławski, W. Knoff, T. Story 

Influence of crystal structure and hole concentration on magnetic anisotropy of 

GeMnTe 

5. I. Ulfat, L. Ilver, J. Sadowski 

High-resolution study of valence band maximum for (GaMn)As 

6. J. Suffczy�ski, K. Gałkowski, P. Ka�mierczak, J. Papierska, M. Furman, W. Pacuski, 

A. Golnik, A.M. Witowski, J.A. Gaj, W. Stefanowicz, M. Sawicki, M. Łukasiewicz, 

E. Guziewicz, M. Godlewski 

Low temperature grown (Zn,Co)O studied in the band-gap spectral region 

7. J. Levrat, G. Rossbach, A. Dussaigne, H. Teisseyre, I. Grzegory, M. Bockowski, 

T. Suski, R. Butte, N. Grandjean 

Nonpolar III-nitride microcavities for polariton lasing 

8. W. Bardyszewski, S.P.. Łepkowski 

Symmetry of the top valence band states in GaN/AlGaN quantum wells and its 

influence on the polarization of emitted light 

9. D. Sztenkiel, T. Dietl 

Tunnelling effects in (Ga,Mn)As based heterostructures 

10. M. Lopuszynski, J.A. Majewski 

Modelling of Ordering Phenomena in Nitride Semiconducting Alloys 

11. M. Welna, R. Kudrawiec, M. Motyka, J. Misiewicz, R. Kucharski, M. Zaj�c, R. 

Doradzi�ski, R. Dwili�ski 

Infrared Spectroscopy of GaN Crystals Obtained by Ammonothermal Method 

12. M. Latkowska, R. Kudrawiec, G. S�k, J. Misiewicz, J. Ibán~ez, M. Henini, 

M. Hopkinson 

Micro-photoluminescence of GaInNAs layers: Thermal quenching of individual 

exciton lines 

13. M. Fandrich, G. Kunert, T. Aschenbrenner, S. Figge, C. Kruse, D. Hommel 

20

40th _______________________________________________________________ 


Nitride based sensors with Ga- and N-polarity 

14. V.Kh. Le, K. Swiatek, M. Pawlowski, R.R. Galazka 

Zinc vacancy induced ferromagnetic interaction in semimagnetic semiconductor 

(Zn,Mn)Te 

15. S. Dobkowska, W. Stefanowicz, O. Proselkov, R. �uberek, J. Sadowski, T. Dietl, 

M. Sawicki 

Magnetic Properties of (Ga,Mn)As near Metal-Isolator Transition 

16. M. Sakowicz, N. Gauthier, R. Leonelli, C. Silva, H. Nguyen, K. Cui, S. Zhang, Z. Mi 

Time-Resolved Photoluminescence of InGaN/GaN Dot-in-a-Wire Heterostructures on 

Si(111) 

17. M. Bajda, F. Dybała, A. Bercha, W. Trzeciakowski, J.A. Majewski 

Wide range wavelength tuning of InGaAsP/InP laser diodes 

18. M. Gryglas-Borysiewicz, J. Przybytek, M. Baj, A. Kwiatkowski, P. Juszy�ski, D. Wasik, 

P. Dziawa, J. Sadowski 

Transport properties of GaMnAs layers 

19. C. Chèze, M. Sawicka, M. Siekacz, H. Turski, A. Feduniewicz-Zmuda, G. Cywinski, B. 

Grzywacz, S. Grzanka, I. Dziecielewski, B. Lucznik, M. Bockowski, C. Skierbiszewski 

Group III-nitrides growth on N-polar substrates 

20. J. Binder, K.P. Korona, J. Borysiuk, M. Kaminska, M. Baeumler, K. Köhler, L. Kirste 

Absorption and Emission Properties of Light Emitting Diode Structures Containing 

GaInN/GaN QWs 

21. B.J. Kowalski, R. Nietuby�, J. Sadowski 

Mn contribution to the valence band of Ga1-xMnxSb 

22. M. Baranowski, M. Latkowska, M. Syperek, R. Kudrawiec, J. Misiewicz, T. Sarmiento, 

J.S. Harris 

Time resolved photoluminescence studies for GaInNAsSb quantum wells emitting at 

1.3 µm 

23. A. Kafar, J. Goss, S. Sta�czyk, R. Czernecki, M. Leszczynski, T. Suski, P. Wi�niewski, 

P. Perlin 

InGaN laser diodes with passive absorber section 

24. W. Szuszkiewicz, F. Ott, J.Z. Domagała, E. Dynowska, J. Sadowski 

Evidence of a new magnetic order in short-period (Ga,Mn)As/GaAs SLs 

25. Z. Wi�niewski, K. Izdebska, P. Sybilski, Z.R. �ytkiewicz, M. Soba�ska, K. Kłosek, 

A. Reszka, B.J. Kowalski, A. Suchocki 

Application of n-GaN layers grown by MBE for light-induced water splitting and 

hydrogen generation 

26. M. Sarzynski, J. Goss, M. Leszczynski, A. Reszka, B. Kowalski, P. Perlin, T. Suski 

21

_______________________________________________________________ 


Broad optical gain spectrum in III-N quantum structures 

27. M.I. Łukasiewicz, A. Cabaj, M. Godlewski, E. Guziewicz, A. Wittlin, M. Jaworski, 

A. Woło�, Z. Wilamowski 

Microwave techniques investigations of (Zn,Co)O films grown by Atomic Layer 

Deposition 

28. O. Yastrubchak, T. Andrearczyk, J. Sadowski, J. �uk, T. Wosi�ski 

Band-structure analysis from photoreflectance spectroscopy in (Ga,Mn)As 

29. K. Klosek, M. Sobanska, Z.R. Zytkiewicz, H. Teisseyre, E. Lusakowska, A. Wierzbicka, 

P. Nowakowski, L. Klopotowski 

Influence of nitrogen plasma parameters on growth of GaN by plasma-assisted 


30. T.A. Krajewski, P. Stallinga, E. Zielony, P. Kruszewski, K. Go�ci�ski, Ł. Wachnicki, 

S. Figge, D. Hommel, E. Guziewicz, M. Godlewski 

Deep defects in ZnO/GaN heterostructure analyzed by the admittance spectroscopy 

31. T.A. Krajewski, A.J. Zakrzewski, G. Łuka, Ł. Wachnicki, S. Gierałtowska, 

B.S. Witkowski, P. Kruszewski, E. Łusakowska, R. Jakieła, E. Guziewicz, M. Godlewski 

Electrical characterization of the ZnO-based Schottky diodes for possible sensor 

applications 

32. T. Zakrzewski, P. Bogusławski 

Ab initio calculations of transition metal impurity levels in III-V semiconductors 

33. P. Juszy�ski, D. Wasik, M. Baj, J. Przybytek, M. Gryglas-Borysiewicz, J. Sadowski 

Anisotropy of GaMnAs thin film. Planar and Anomalous Hall measurements. 

34. G. Staszczak, A. Khachapuridze, S. Grzanka, R. Piotrzkowski, R. Czernecki, P. Perlin, 

T. Suski 

Interplay between internal and external electric field studied by photoluminescence in 

InGaN/GaN light emitting diodes 

35. M. Baranowski, M. Latkowska, R. Kudrawiec, M. Syperek, J. Misiewicz, 

G.S. Karthikeyan, S. Jong-In, K.L. June 

Influence of antimony on the optical quality of GaInN:Sb multi quantum wells 

36. J. Sadowski, A. Siusys, P. Dziawa, A. Reszka, B.J. Kowalski 

Properties of Mn-doped GaAs Nanowires and GaAs/(Ga,Mn)As Core-Shell Nanowire 

Structures Grown by MBE on GaAs(111)B Substrates 

37. I.A. Kowalik, M.A. Nin~o, A. Locatelli, T. OnurMente�, A. Navarro-Quezada, 

M. Rovezzi, A. Bonanni, T. Dietl, D. Arvanitis 

Room temperature nano-magnetism of (Ga,Fe)N films: element specific spectroscopy 

and microscopy 

38. L. Marona, S. Grzanka, P. Wisniewski, T. Suski, M. Leszczynski, R. Czernecki, 

M. Bockowski, S.P. Najda, P. Perlin 

22

40th _______________________________________________________________ 


The non-radiative recombination rate in InGaN laser diodes during the aging 

39. L. Janicki, M. Gladysiewicz, R. Kudrawiec, M. Rudzi�ski, R. Kucharski, M. Zaj�c, 

J. Misiewicz, W. Strupinski, R. Doradzi�ski, R. Dwili�ski 

Electromodulation Spectroscopy of GaN/AlGaN Quantum Wells Grown on Polar and 

Non-polar GaN Substrates Obtained by Ammonothermal Method 

40. E.P. Smakman, R. vanVoornveld, J.G. Keizer, J.K. Garleff, P.M. Koenraad 

Spin-Polarized STM with Fe-Coated W Tips and Bulk Cr Tips 

41. B.S. Witkowski, Ł. Wachnicki, E. Guziewicz, M. Godlewski 

Cathodoluminescence measurements at liquid helium temperature of monocrystalline 

ZnO layers 

42. T. Andrearczyk, I. Krogulec, T. Wosi�ski, T. Figielski, A. M�kosa, Z. Tkaczyk, 

J. Wróbel, J. Sadowski 

Towards electrically controllable read-write devices based on ferromagnetic 

semiconductors 

43. J.B. Gosk, Z. Werner, C. Pochrybniak, M. Barlak, J. Szczytko, A. Twardowski 

Magnetic properties of Mn-ion implanted and plasma pulse treated Si 

44. G. Muzioł, M. Siekacz, H. Turski, C. Skierbiszewski 

Simulations of optical modes in InGaN based laser diodes operating at 455 nm 

45. M. Woi�ska, K. Madrak, J. Szczytko, J. Gosk, A. Majhofer, D. Pociecha, E. Górecka, 

A. Twardowski 

Monte-Carlo simulations and magnetic studies of ferromagnetic nanocomposites 

46. J. Szczytko, J. Szydlowska, N. Gonzalez Szwacki, K. Dziatkowski, P. Gizi�ski, A. Kaim, 

A. Twardowski 

Di-TEMPO amine for molecular spintronics – model of p-shell magnetism 

47. M. Baranowski, M. Latkowska, R. Kudrawiec, J. Misiewicz 

Hopping excitons in GaInNAs alloys: Radiative versus non-radiative recombination at 

various temperatures 

48. J.Z. Domagala, B. Lucznik, H. Teisseyre, M. Bockowski, I. Grzegory 

Structural characterization of the nonpolar substrate grown by multistep hydride vapor 

phase epitaxy. 

49. Ł. Gluba, O. Yastrubchak, H. Krzy�anowska, J.Z. Domagała, T. Andrearczyk, J. �uk, 

J. Sadowski, T. Wosi�ski 

Investigation of fundamental parameters of low doped (Ga,Mn)As epitaxial layers 

50. P. Kamyczek, E. Popko, Z. Gumienny, E. Zielony, S.Grzanka, R. Czernecki, T. Suski 

Admittance spectroscopy in GaN p-n junction 

51. Pawel Kempisty, Pawel Strak, Stanislaw Krukowski 

23

_______________________________________________________________ 


Role of hydrogen in the ammonia based growth of GaN and InGaN - ab initio study 

52. S.P. Lepkowski, W. Bardyszewski, H. Teisseyre 

Effect of the built-in strain on the in-plane optical anisotropy of m-plane GaN/AlGaN 

quantum wells 

53. J. Papierska, J.-G. Rousset, A. Golnik, W. Pacuski, M. Nawrocki, J. A. Gaj, 

J. Suffczynski, I. Kowalik, W. Stefanowicz, M. Sawicki, T. Dietl, A. Navarro-Quezada, 

B. Faina, Tian Li, A. Bonanni 

Magnetooptical properties of (Ga,Fe)N layers 

54. Maria Ptasi�ska, Jacek Piechota, Jakub Sołtys, Stanisław Krukowski 

Gas Phase Reactions during GaN Growth by MOVPE Method – Ab initio Study 

55. Konrad Sakowski, Leszek Marcinkowski, Szymon Grzanka, Elzbieta Litwin- 

Staszewska, Stanislaw Krukowski 

Simulations of Gallium Nitride luminescent devices with extension of standard 

nonradiative recombination model 

56. Pawel Strak, Pawel Kempisty, Konrad Sakowski, Stanislaw Krukowski 

Density Functional Theory (DFT) simulations of the physical properties of AlN/GaN 

multiple quantum wells (MQWs) 

57. Z. R. Zytkiewicz, P. Dluzewski, J. Borysiuk, M. Sobanska, K. Klosek, B. Witkowski, 

P. Nowakowski, J. Dabrowski 

Plasma-assisted MBE growth and characterization of GaN nanocolumns on Si (111) 

substrates 

58. Zbigniew R. Zytkiewicz, Pawel Strak, Stanisław Krukowski 

Crossing Size Limits of Bulk III-V Crystals Feasible by Liquid Phase Electroepitaxy 

24

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors SaI1 

Modern technologies for wide-gap semiconductor epitaxy 

and nano-processing 

Detlef Hommel 

Institute of Solid State Physics, University of Bremen, Germany 

An overview will be given on the growth and application of wide bandgap 

semiconductors like group-III nitrides and group-II selenides and tellurides. It will be shown 

that different epitaxial methods have to be used for different materials (MBE for II-VI and 

mostly MOVPE for nitrides). In this respect homo- and heteroepitaxy will be compared as 

well. 

The growth mechanisms for CdSe and InGaN quantum dots differ significantly and 

both have not much common with the well known Stranski-Krastanov growth mode. This will 

be discussed in detail. 

As an important tool for nano-processing a focused ion beam (FIB) tool will be 

presented. Such a dual beam system with a Ga-source for nanostructuring, an electron source 

for imaging, an integrated e-beam lithography and sources for insulator and metal deposition 

on a nanometer scale allows to design novel device structures. 

Approaches to grow fully monolithic microcavities based on selenides, nitrides and 

tellurides will be presented. Using the FIB micropillars can be designed out of such planar 

structures with interesting physical properties. Introducing quantum dots into the cavity one 

can obtain efficient sources for single photon emission up to room temperature. 

25

SaI2 _______________________________________________________________ 


Physical simulation of electronic devices 

Aldo Di Carlo 

Dept. of Electronics Engineering, University of Rome “Tor Vergata”, Rome, Italy 

Physical Simulation is a fundamental step for the design and fabrication of 

commercially available and research developed electronic devices.[1] Since ’80 several 

Technology Computer Aided Design (TCAD) tools has been developed to this end, starting 

from the seminal work of R. Dutton at Stanford University. Nowadays, the need for faster 

and better performing electronic devices with higher integration density has been driving 

almost since the dawn of semiconductor technology a steady trend of scaling down the device 

dimensions. This led to an incredible increase in computing power and memory capacity, 

quantified by the well-known Moore’s law. Due to this downscaling, the dimensions of the 

active region of conventional metal–oxide–semiconductor field-effect transistors (MOSFETs) 

have already reached the nanometer scale. This makes device simulation very challenging and 

new theoretical framework should be considered. [2] 

Hand in hand with device scaling, new devices exploiting quantum mechanical effects for 

their functioning have been proposed, e.g., transistors based on quantum wires, dots, or 

molecules. Quantum dots and wires have also gained much attention for their use in 

optoelectronic devices for lasing or single photon emission or as color tunable and white-light 

emitters. The electronic, optical, and transport properties of the active regions of such highly 

scaled or new devices cannot be described by classical or semiclassical theories. A fully 

quantum mechanical treatment has to be used instead. [3] 

In this lecture, I will review the methods for electronic device simulation starting from the 

common picture based on drift-diffusion equation up to quantum mechanical based 

approaches for both continuum and atomistic models. A review of available TCAD tools will 

be given. 

Fig. 1 

Simulation of GaN based nanocolumn LED. 

Electrostatic potential and current flow lines 

around the intrinsic part of the column. 

(a) The classical results. 

(b)The self-consistent Quantum/driftdiffusion 

results, showing also the contours of the electron 

and hole densities at half of the mean density 

inside the intrinsic region. (from Ref. 2) 

[1] S. Selberherr, Analysis and Simulation of Semiconductor Devices, Springer, (1984). 

[2] M. Auf der Maur et al. IEEE Trans. Electron Devices 58, 1425 (2011) 

[3] A. Pecchia and A. Di Carlo, Rep. Prog. Phys., vol. 67, no. 8, pp. 1497–1561, (2004). 

26

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors SuI1 

Physics and Technology of Arsenide Based Quantum Dots and Nanowires 

Gerhard Abstreiter 

Walter Schottky Institut and Institute for Advanced Study 

TU München, 85748 Garching 

Optical control of charges, spins, excitons and photons has been achieved in recent years in 

semiconductor nanostructures. They are therefore excellent candidates for demonstrating 

basic principles of quantum information technology. I will discuss the basic optical properties 

and recent results on electro-optic control of single self-assembled InGaAs quantum dots. 

This includes results on spin storage and spin lifetimes of electrons and holes [1, 2] in dot 

ensembles, as well as single charge and spin control and readout [3]. In the second part of my 

lecture I will also discuss recent results on MBE grown GaAs and InAs based nanowire 

hetero-structures with new functionalities [4 - 9]. 

[1] M. Kroutvar et al., Nature 432, 81 (2004) 

[2] D. Heiss et al., Phys. Rev. B 76, 24136 (2007) 

[3] D. Heiss et al., Phys. Rev. B 82, 245316 (2010) 

[4] A. Fontcuberta i Morral et al., Small 4, 899 (2008) and APL 92, 063112 (2008) 

[5] M. Heigoldt et al., J. Mater. Chem. 19, 840 (2009) 

[6] D. Spirkoska et al., Phys. Rev. B 80, 245325 (2009) 

[7] I. Zardo et al., Phys. Rev. B 80, 245324 (2009) 

[8] S. Hertenberger et al., J. Appl. Phys. 108, 114316 (2010) 

[9] M. Soini et al., Appl. Phys. Letters 97, 263107 (2010) 

27

SuI2 _______________________________________________________________ 


Tutorial: Engineering of Electric Fields in Nitride-Based Semiconductors 

Debdeep Jena 

Associate Professor of Electrical Engineering University of Notre Dame, 

Notre Dame, IN 46556 USA 

djena@nd.edu, http://www.nd.edu/~djena 

The built-in polarization fields in III-Nitride semiconductor heterostructures play 

fundamental and crucial roles in many electronic and optical phenomena exhibited by these 

semiconductors. In addition, they strongly influence the design and performance of electronic 

and optical devices fabricated from III-Nitride heterostructures. The goals of this tutorial are – 

1) To introduce the concept of electronic polarization in semiconductors 

2) To explore its influence on electronic and optical properties 

3) To explore details of how charge electrostatics and transport are affected 

4) To explore how optical transitions and emission properties are influenced, 

5) To apply them to electronic and optical devices of the present, and 

6) To discuss open problems, and what is possible in the future using polarization. 

Specifically, the concept of polarization will be traced down to its microscopic origin in 

charge dipoles in the highly polar III-Nitride semiconductor crystals. We will discuss how the 

macroscopic properties emerge from the microscopic picture. The effect of dipoles on charge 

transport, electrostatics, and optical transition matrix elements will be described. We will 

study how the fields emerging from the polarization can be used to design ‘traditional’ highperformance 

electronic and optical devices such as high electron mobility transistors 

(HEMTs), light-emitting diodes (LEDs) and lasers. The discussion will cover both the ‘good’ 

and ‘bad’ effects of polarization in such devices. 

We will also discuss various “novel” device applications of polarization physics in III- 

Nitride semiconductor heterostructures. Some of these include polarization-induced Zenerinterband 

tunneling and p-type doping for applications in light emitting devices. The wellknown 

concept of “lattice-- matching” in III-V semiconductor heterostructures will be 

extended to include the idea of “Polarization-- matching” and the opportunities of such 

concepts will be discussed. 

28

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors MoI1 

�� 

Coherent optical control of the NV center in diamond 

Jörg Wrachtrup 

3rd� Physics Institute and Research Center SCOPE, University of Stuttgart, D-70659 

Stuttgart, Germany 

29

MoI2 _______________________________________________________________ 


Understanding and exploiting magnetism of semiconductors 

Tomasz Dietl 

Laboratory for Cryogenic and Spintronic Research, 

Institute of Physics, Polish Academy of Sciences and 

Institute of Theoretical Physics, University of Warsaw 

Triggered by a theoretical model of ferromagnetism mediated by valence band 

holes put forward a dozen years ago, the search for compounds combining the resources 

of semiconductors and ferromagnets has evolved into an important and challenging field 

of materials science. This endeavour has been fuelled by continual demonstrations of 

remarkable low-temperature functionalities found for ferromagnetic structures of 

(Ga,Mn)As, p-(Cd,Mn)Te, are related materials -- now transferred to elemental 

ferromagnets -- as well as by abundant experimental observations and theoretical 

modellings of ferromagnetic features persisting up to high temperatures in a number of 

magnetically doped semiconductors and oxides without any valence band holes or even 

in materials nominally undoped with transition metals. 

In the talk, a broad overview of recent breakthrough experimental and theoretical 

developments will be given emphasizing that, from the one hand, they disentangle 

controversies and puzzles accumulated over the last decade and, on the other, offer new 

outstanding research prospects [1]. More specifically, it will be shown how element 

specific and spin sensitive contemporary nanocharacterization methods help to asses the 

real structure of materials down to the atomic scale and, thus, to build a sensible 

theoretical understanding of macroscopic properties, including the origin of low- and 

high-temperature ferromagnetism in semiconductors. Recent experiments that 

demonstrate the influence of the electric field and current on magnetism and the 

generation of current by time-dependent magnetization will be discussed in a broad 

context of spin physics and spintronic applications. 

[1] See, T. Dietl, “A ten-year perspective on dilute magnetic semiconductors and oxides”, 

Nature Mater. 9, 965 (2010). 

30

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors MoI3 

Charging Effects in Self Assembled CdTe Quantum Dots 

Łukasz Kłopotowski 

Institute of Physics, Polish Academy of Sciences al. Lotników 32/46, Warszawa, Poland 

Semiconductor quantum dots (QDs) are often referred to as artificial atoms. This 

analogy stems mostly from zero dimensional density of states hindering interactions between 

these nanostructures and the environment. In fact, QDs are more than atom-like 

structures: they can be easily incorporated into semiconductor devices enabling studies 

of properties impossible to achieve in atom particles. These phenomena are related to 

a possibility of controllable feeding the dots with charge carriers one by one: an effect 

resulting from a Coulomb blockade. Such deterministic charging not only allows to study 

effects related to Coulomb interaction between carriers, but has proved to be essential 

in discoveries of phenomena requiring a particular QD charge state: creation of dynamic 

nuclear polarization, coherent qubit operations, creation of Mahan excitons, to name just 

a few. 

Most studies on charge tunability of QDs were done in InGaAs system. On the other 

hand, II - VI QDs possess a few interesting advantages over their better known counterparts: 

they can be easily doped with magnetic ions and exhibit stronger excitonic 

interactions. Combining these features with a possibility to prepare a II - VI QD in 

a given charge state can result for instance in electrical control over magnetism on a 

nanoscale. 

In this talk, we report on our recent achievements in studies of charging effects in 

self assembled CdTe QDs [1]. By studying QD photoluminescence (PL), we show charge 

tunability in dots embedded in a field-effect structure. Exploiting the vertical electric 

field resulting from biasing the device, we study the quantum confined Stark effect to 

gain insight into Coulomb interactions and changes of charge distribution upon tuning 

the QD occupancy. In particular, we find that the electron wave function is stiffer than the 

hole wave function – an effect which we subsequently confirm with analysis of PL lifetimes 

of different QD occupancies. We demonstrate that the confinement in our dots is far from 

the strong confinement limit. This in turn results in Coulomb correlations dominating 

over confinement. A fingerprint of this phenomenon is a universal shape of the QD PL 

spectrum featuring the same transition sequence – an effect entirely different from the 

InGaAs system, where confinement conditions totally determine the PL spectrum. We 

conclude with presenting an outlook for future studies involving magnetically doped dots 

and different approaches for extending the tunability in this system. 

[1] Ł. Kłopotowski et al. Phys. Rev. B 83, 155319 (2011). 

31

MoI4 _______________________________________________________________ 


Optical properties of strongly in-plane asymmetric epitaxial nanostructures 

Grzegorz Sęk 

Institute of Physics, Wrocław University of Technology 

Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland 

Strongly laterally asymmetric nanostructures have already been proven advantageous in 

both laser applications, offering higher gain and broader spectral tunability, or fundamental 

studies of solid state quantum electrodynamics (QED), due to enhanced exciton oscillator 

strength. On the other hand, such structures are believed to have selective and geometrydriven 

polarization properties. However, our spectroscopic measurements on self-assembled 

structures of two material systems but similar geometries (lateral aspect ratio of about 3-5) 

demonstrated significantly different properties. 

For InAs elongated structures (called dashes) on InP substrate the linear-polarizationresolved 

photoluminescence measurements have shown the degree of polarization (DOP) at 

the level of 30% for high excitation conditions and/or at elevated temperatures. A systematic 

increase of the DOP has been observed for the enlarged dash height and eventually exceeded 

90% for very tall structures called columnar quantum dashes. The dependence, tending to 

saturate for larger heights, has been reproduced theoretically by both analytical considerations 

assuming the heavy - light hole bands mixing as the primary factor responsible for the 

polarization properties and by full 8 band kp calculations including strain. Unexpectedly 

however, low temperature single dot study revealed exciton to biexciton lifetimes ratio of 

about 2 and biexciton binding energy below 0.5 meV, both together characteristic for the 

strong confinement regime. In addition, rather small exciton fine structure splitting in the 

range of 60 – 200 µeV has been detected, comparable to values reported for common selfassembled 

dots. All these facts suggest the occurrence of an additional exciton localization 

within the structures, e.g. on local size or content fluctuations, causing a decreased 

confinement anisotropy. This has further been supported by an observed decrease of the DOP 

down to about 10% at low temperatures and low excitation. The calculated temperature 

dependence of the DOP reproduced this feature very well after taking into account a 

fluctuation of the dash cross-sectional size. The latter confirmed that the low temperature 

emission originates from excitons trapped on potential fluctuations with the localization 

energy of about 5 meV. 

Quite an opposite behavior has been found for In0.3Ga0.7As/GaAs extended quantum 

dots. On one hand, single dot study, QED experiments on a dot inside a pillar microresonator 

and time-resolved spectroscopy have shown large oscillator strengths and weakened quantum 

confinement manifested in a small value of the exciton to biexciton lifetime ratio (below 1) 

and a decreased (as compared to standard quantum dots) exciton radiative lifetime (~ 300 ps). 

Further, we observed no fingerprints of any localization effects in the polarization-resolved 

experiments versus temperature and excitation, which agrees with a very smooth morphology 

of these structures when compared to the InP-based ones. The DOP is only about 6% despite 

the shape asymmetry and similar light hole contribution to valence band states as in InP-based 

structures (based on 8 band kp calculations). This is caused by a shallow electron confining 

potential making them (and hence the entire exciton) to experience less anisotropic 

confinement potential. Furthermore, exciton localization within the wetting layer enhancing 

their radiative lifetime to almost 1 ns has been observed. This appeared to be responsible for 

strong temperature sensitivity of the wetting layer - quantum dot energy transfer efficiency 

and the appearance of a low-energy sideband emission accompanying the biexciton, being a 

fingerprint of its interaction with excitons from the wetting layer. 

32

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors MoO1 

Coupling between electronic and vibrational excitations in 

carbon nanotubes filled with C60 fullerenes 

Pawel Utko 1 , Raffaello Ferone 2,3 , Ilya V. Krive 3,4 , Robert I. Shekhter 3 , Mats 

Jonson 3,5,6 , Marc Monthioux 7 , Laure Noé 7 , and Jesper Nyg˚ard 1 

1 Niels Bohr Institute & Nano-Science Center, University of Copenhagen, 

DK-2100 Copenhagen, Denmark 

2 Department of Physics, Lancaster University, Lancaster LA1 4YB, UK 

3 Department of Physics, University of Gothenburg, SE-412 96 Göteborg, Sweden 

4 B. I. Verkin Institute for Low Temperature Physics and Engineering, 

61103 Kharkov, Ukraine 

5 School of Engineering and Physical Sciences, Heriot-Watt University, 

Edinburgh EH14 4AS, UK 

6 School of Physics, Konkuk University, Seoul 143-701, Korea 

7 CEMES-CNRS, B.P. 94347, F-31055 Toulouse Cedex 4, France 

Filling single wall carbon nanotubes with C60 fullerenes yields hybrid structures [1], 

the so-called C60 fullerene peapods, which can offer enhanced functionality with respect 

to empty tubes. Prospective nanoelectronic applications of such composites include data 

storage devices, single electron transistors and spin-qubit arrays for quantum computing. 

However, the extent to which the electronic properties of peapods are affected by 

entrapped fullerenes is still unclear. Even though theoretical investigations predict dramatic 

changes in the electronic band structure of the nanotube, the experimental results 

remain equivocal. 

Here, we investigate the effect of the C60 fullerenes on the low-temperature electron 

transport via peapod quantum dots [2] operated in the regime of weak electronic coupling 

Γ between energy states of the dot and its electrical leads. Compared with empty nanotubes, 

we find an abnormal temperature dependence of Coulomb blockade oscillations, 

indicating the presence of a nanoelectromechanical coupling between electronic states of 

the nanotube and mechanical vibrations of fullerenes. This provides a useful method to 

detect the C60 presence and to probe the interplay between electrical and mechanical 

excitations in peapods, which thus emerge as a new class of nanoelectromechanical systems. 

We note that other types of devices for which a coupling to mechanical vibrations 

plays a crucial role in electrical transport are suspended nanotubes, as well as molecular 

conductors and transistors. 

[1] B. W. Smith, M. Monthioux, and D. E. Luzzi, Nature 396, 323 (1998). 

[2] P. Utko, R. Ferone, I. V. Krive, R. I. Shekhter, M. Jonson, M. Monthioux, L. Noé, 

and J. Nyg˚ard, Nature Commun. 1, 37 (2010). 

33

MoO2 _______________________________________________________________ 


Solid-state self assembly: a route to hybrid metal-semiconductor epitaxial 


Adam Urba�czyk, Frank W.M. van Otten and Richard Nötzel 

COBRA Research Institute, Departament of Applied Physics, Eindhoven Univeristy of 

Technology, The Netherlands 

� 

� 

Recently there has been a lot of research interest in metallic nanostructures for 

confining light at deeply subwavelength dimensions utilizing surface plasmons. Such 

plasmonic nanostructures are currently finding applications in fields of sensing and energy 

conversion. Combining them with optically active media such as semiconductor quantum dots 

(QDs) could lead to even more exciting applications in the field of nanophotnics and 

nanoelectronics, where the metal-QD hybrid structures could be used as ultrasmall light 

sources or switching elements. In order to obtain such hybrid structures in reproducible and 

scalable manner one has to control the metal-QD separation with single nanometer precision 

owing to extreme light confinement due to surface plasmon resonance (SPR). Recently our 

group demonstrated a promising approach to solve this problem by utilizing solid-state selfassembly. 

Here we report alignment of epitaxial nanocrystals of Ag and In on isolated InAs 

QDs and one dimensional QD arrays obtained by molecular beam epitaxy (MBE). By 

changing the process conditions the SPR wavelength of the metal nanocrystals can be easily 

tuned over wide range in order to match the emission wavelength of the QDs. 

Photoluminescence (PL) measurements reveal large enhancement of the emitted light 

intensity as compared to a reference structure without metal. What is more, in those hybrid 

nanostructures PL polarization is modified, evidencing electromagnetic character of the 

interaction between the metal nanocrystals and the QDs. 

� 

Figure 1. Atomic force microscope image of a Ag nanocrystas aligned on a single near-surface 

InAs QD and a reference structure with bare near surface QDs. 

34

40th _______________________________________________________________ 


First-Principles Study of Doped III–V nanowires 

M. Galicka 1 , P. Kacman 1 and R. Buczko 1 

1 Institute of Physics PAS, al. Lotników 32/46, 02-668 Warsaw, Poland 

GaAs and InAs nanowires (NWs) are considered as one of the most interesting structures for 

nanoelectronics and nanophotonics. Their potential application in novel electronic devices 

requires, however, controllable p-type and n-type conductivity. The specific growth conditions 

for NWs, their crystal structure and orientation of their side facets lead sometimes to different 

incorporation of dopants than known for planar layers. For example, GaAs epitaxial layers are 

typically p-type doped with Be and n-type doped with Si ions. In contrast, in GaAs NWs 

although Si doping leads sometimes to n-type, but most often p-type conductivity is observed 

in Si-doped GaAs NWs [1,2]. The problem of doping of NWs has become now a major 

challenge to the growers of one-dimensional III-V semiconductor structures. 

To explain the observed phenomena we study theoretically the properties of GaAs and 

InAs NWs, in which one cation/anion is substituted by a dopant ion. Since the III-V 

semiconductor NWs can grow in both, zinc-blende (ZB) and wurtzite (WZ) structures, we 

check whether the crystal structure of the wire has an impact on the doping level and the 

distribution of impurities in the NW and, most important, on the electronic properties of the 

doped NWs. The calculations show that the distribution of impurities in the wires as well as 

the conductivity depend crucially on the crystal structure. 

We consider ZB NWs oriented along (111) axis and WZ NWs along (0001) axis. These 

growth directions are chosen because they are the most energetically preferred for both GaAs 

and InAs NWs [3]. Using ab initio methods based on the density functional theory we have 

calculated the formation and segregation energies for GaAs and InAs NWs doped with 

different ions. In GaAs NWs, we consider Be atom, which substitutes a cation and should lead 

to p-type conductivity and Si atom which substitutes either anion (p-type) or cation (n-type). 

The formation energies for Si in GaAs NWs calculated for various sets of chemical potentials 

suggest that the energy needed for substituting the anion and the cation, and thus the type of 

conductivity obtained by Si-doping, can be different in ZB and WZ wires. As-grown InAs 

NWs have usually high concentration of electrons in the conduction band. Thus, in InAs NWs 

we show, by comparing the formation energies, that among Be, Zn or Si impurities, which can 

be used to obtain p-type wires, Be is preferred. 

The segregation energy shows where the dopants prefer to stay – it is defined as the 

difference between the energy of a NW with the impurity ion in a given position in the wire 

and in its center. It has been obtained that in ZB structures the impurities prefer to stay at the 

side surfaces of the NW. In WZ NWs the positions inside the wire are preferred. For all kinds 

of impurities studied, the segregation energy in WZ NWs is much smaller than in ZB NWs, 

thus, the distribution of impurities in WZ wires should be much more homogenous. 

To study the electronic properties we have calculated the density of states of the doped 

NWs. In contrast to the formation and segregation energies, which have been calculated for 

wires with the surfaces not saturated by foreign ions, the density of states has been obtained 

for wires with side surfaces fully passivated by hydrogen atoms. 

[1] M. Hilse et al., Appl. Phys. Lett. 96, 193104 (2010) 

[2] J. Dufouleur et al., Nano Lett. 10, 1734 (2010) 

[3] M. Galicka, et al., J. Phys: Condens. Matter 20, 454226 (2008) 

Work supported by EC network SemiSpinNet (PITN-GA-2008-215368). 

35

MoO4 _______________________________________________________________ 


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36

40th _______________________________________________________________ 


Growth of optically active CdTe quantum dots in ZnTe nanowires 

� 

P. Wojnar 1 , E. Janik 1 , S. Kret 1 , A. Petrouchik 1 , M. Goryca 2 , 

T. Kazimierczuk 2 , P. Kossacki 2 , G. Karczewski 1 and T. Wojtowicz 1 

� 

1 Institute of Physics, Polish Academy of Sciences, Al Lotników 32/46, 02-668 Warsaw, Poland 

2 Institute of Experimental Physics, University Warsaw, ul Ho�a 69, 00-681 Warsaw, Poland 

Quantum dots consisting of nanometer sized insertions of low energy gap semiconductor in large 

energy gap nanowire have recently risen a great interest because of their emerging applications as 

single photon sources at room temperature [1], biological markers, nanobarcodes [2] and also in view 

of electronic coupling of several quantum dots. 

In this work the growth and optical properties of CdTe 

quantum dots in ZnTe nanowires are reported. The structure is 

grown by molecular beam epitaxy in the vapor-liquid-solid 

growth mechanism induced by gold catalysts. Nanometer sized 

droplets of gold/gallium eutectic are formed on GaAs substrate 

by thermal treatment of a 1 nm thick gold layer deposited in a 

separate growth process. Subsequently, ZnTe nanowires with 

the length of about 1.5 �m are grown at relatively high 

substrate temperature of 420°C. For the deposition of the CdTe 

insertion, the temperature is decreased to 380°C, which is still 

a too high temperature for the epitaxial growth and, therefore, 

ensures that CdTe growth occurs in the axial direction of the 

nanowire. Deposition time of CdTe is set to 60s. The further 

growth of 200 nm ZnTe nanowire segment takes place at 

380°C. 

Photoluminescence measurements performed at 5 K show 

clearly that the presence of CdTe insertions in the ZnTe 

nanowires results in the appearance of a strong emission in the 

2.0 eV – 2.2 eV energy region. When the excitation spot 

Figure Low temperature micro- 

photoluminescence of the ZnTe 

nanowires with CdTe insertions – 

(a) “as grown” sample - several objects 

excited simultaneously (b) nanowires 

dispersed on silicon – only one 

emission line present, 9 K, excitation: 

532 nm (2.33 eV), 100 �W 

diameter is reduced to the size of the order of 1 �m, this broad 

band splits into several sharp lines with the spectral width of 

the order of 2 meV, figure a. Those lines are related to the 

emission from individual quantum dots in nanowires as 

confirmed by our further study. In order to better resolve the 

individual emission lines, the nanowires are removed from the 

GaAs substrate in a ultrasonic methanol bath and dispersed on 

a silicon substrate, figure b. 

The emission lines exhibit a relatively large degree of linear 

polarization ranging from 70% to 95% depending on the particular line. This effect is due to large 

contrast of the dielectric constant of the nanowire and the surrounding and, thus, confirms that the 

emissions come from an object placed inside a nanowire. On the other hand, photon correlation 

measurements prove the zero dimensional character of studied objects. A clear antibunching at the zero 

delay time between arriving of two subsequent photons from the same emission line is observed 

confirming that these individual objects cannot emit simultaneously two photons at the same energy. 

Moreover, the power dependence of the emission and the cross-correlation measurements allow us to 

indentify biexcitonic emissions with binding energies ranging from 7 - 12 meV 

The research has been supported by the European Union within European Regional Development Fund through Innovative 

Economy grant (POIG.01.01.02-00-008/08) and “support for the creation of joint research infrastructure of scientific 

institutions.” - POIG.02.02.00-00-003/08 

[1] A. Tribu et al., NanoLett., 8, 4326 (2008) 

�� 

37

MoO6 

_______________________________________________________________ 


Electronic properties of graphite 

J. M. Schneider 1,2 , B. A. Piot 2 , I. Sheikin 2 , N. A. Goncharuk 3 , P. Vaˇsek 3 , P. Svoboda 3 , Z. Výborný 3 , L. Smrčka 3 , 

M. Orlita 2 , M. Potemski 2 , and D. K. Maude 2 

1 Instituto de Física, Universidade de São Paulo, PB 66318, 05315-970 São Paulo, SP, Brazil 

2 Grenoble High Magnetic Field Laboratory, Centre National de la Recherche Scientifique, 38042 Grenoble, France 

3 Institute of Physics, Academy of Science of the Czech Republic, 162 53 Prague 6, Czech Republic 

Despite more than 50 years of reserach, graphite is not yet fully understood. From the viewpoint of graphene, a 

single layer of carbon atoms set in a honeycomb lattice, graphite can be considered as a quasi-two-dimensional (2D) 

system consisting of a macroscopic stack of graphene layers. A fundamental question concerns the link between 

the coupling of the graphene layers and the dimensionality of the electronic system in graphite. According to the 

Slonczewski, Weiss, and McClure (SWM) band structure calculations of graphite the weak coupling leads to the form 

of the in-plane dispersion depending upon the momentum kz in the direction perpendicular to the layers. The carriers 

occupy a region along the H-K-H edge of the hexagonal Brillouin zone. The Fermi surface of graphite reveals two 

extremal majority charge carriers cross sections: Electrons at the K point (kz = 0) and holes at kz = 0.35. For both 

types of charge carriers the in-plane dispersion is parabolic (massive fermions). Only at the H point (kz = 0.5) the 

in-plane dispersion is linear, similar to that of charge carriers in graphene (massless Dirac fermions). However, the 

extremal cross section at the H point is negligible (minority charge carriers) and does not contribute significantly to 

the electronic properties of graphite. 

This work represents a review of recent studies of the electronic properties of graphite using the Shubnikov-de Haas 

(SdH) and the de Haas -van Alphen (dHvA) effect at millikelvin temperatures [1, 3–5]. Because of the low temperatures 

used, both the SdH and the dHvA effect are much richer than previously published data. Quantum oscillations 

are observed for both majority electrons and holes with an orbital quantum number up to almost N = 100. The 

high quality of the data allows a detailed investigation of the fine structure of the Fermi surface [1]. Using both the 

semiclassical model and the full magnetic field Hamiltonian we show that these oscillations are fully consistent with 

the three-dimensional (3D) SWM bandstructure calculations of graphite. At magnetic fields B > 2 T, a significant 

deviation from the 1/B periodicity occurs. A self-consistent calculation of the Fermi energy shows that the deviation 

from the 1/B periodicity is caused by a considerable movement of the Fermi energy when the quantum limit is approached. 

This seriously questions the validity of using the high-field data to extract the phase of the Shubnikov-de 

Haas oscillations and hence the nature of the charge carriers [2, 3]. The detailed information of the band structure 

of graphite and the movement of the Fermi energy in magnetic field allows to examine the spin splitting of quantum 

features. We show that an effective g-factor value of g ∗ = 2.5 is required to explain the data [4]. 

We performed dHvA measurements to make a complete map of the Fermi surface of graphite. For tilt angles θ < 60 ◦ , 

the fundamental frequencies of both the electrons and holes follow almost exactly a 1/cos(θ) dependence (quasi-2D 

behavior). For θ > 60, a clear deviation from the quasi-2D behavior is observed. The deviation is a signature of 

the dispersion along kz and unequivocally demonstrates the 3D character of the Fermi surface which arises from the 

coupling between the graphene layers. Furthermore, the observation of quantum oscillations at θ = 90 ◦ is a direct 

proof that the Fermi surface of graphite is closed. Additionally, the θ = 90 ◦ data reveals minority holes with a Dirac 

like energy spectrum much like as for charge carriers in graphene [5]. 

References 

[1] J. M. Schneider, Phys. Rev. Lett. 102, 166403 (2009). 

[2] I. A. Luk’yanchuk and Y. Kopelevich, Phys. Rev. Lett. 97, 256801 (2006). 

[3] J. M. Schneider, Phys. Rev. Lett. 104, 119702 (2010). 

[4] J. M. Schneider et al, Phys. Rev. B 81, 195204 (2010). 

[5] J. M. Schneider, to be submitted to Phys. Rev. Lett. 

38

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors MoP1 

Nonlocal transport in PbTe/PbEuTe microstructures 

K. A. Kolwas 1 , G. Grabecki 1,2 , S. Trushkin 1 , Ł. Cywiński 1 , M. Aleszkiewicz 1 , 

T. Dietl 1,3 , G. Springholz 4 , G. Bauer 4 

1 Instytut Fizyki PAN, al. Lotnikow 32/46, PL-02-668 Warszawa, Poland 

2 Wydział Matematyczno-Przyrodniczy, Szkoła Nauk Ścisłych, UKSW, ul. Wóycickiego 1/3, 

PL 01-938 Warszawa, Poland 

3 Instytut Fizyki Teoretycznej, UW, ul.Hoża 69 PL 00-681 Warszawa, Poland 

4 Institut für Halbleiter-und-Festkörperphysik, Johannes Kepler University, 

Altenbergerstr. 69, A-4040 Linz, Austria) 

Heterostructures of narrow-gap semiconductors have recently received a renewed attention, due to the discovery 

of Quantum Spin Hall phase in HgTe/HgCdTe quantum wells [1], the fingerprint of which is the presence of 

large quantized nonlocal voltage signals due to the edge currents [2]. However, even in the topologically trivial 

phase, a large nonlocal voltage signal has been seen in Hall bar structures of HgTe [3] due to the presence of 

Spin Hall Effect (SHE) in the ballistic regime [4]. 

Heterostructures of IV-VI compounds (Pb,Eu,Sn)Te are another attractive candidates in which one can 

search for physics related to the crucial influence of the spin-orbit coupling on the electronic structure of 

relevant bands. In contrast to HgTe case, there is no inversion asymmetry (because of rock-salt crystal structure) 

and the Dresselhaus splitting is absent. The huge dielectric constant of PbTe (e0 > 1000) makes it an ideal 

material in which quantum ballistic transport effects can be observed [5]. 

We have fabricated, by means of the e-beam 

lithography techniques, multi-probe quantum wires (see 

Fig. 1 inset) based on an MBE-grown PbTe quantum 

well (QW), of the thickness of 12 nm, embedded 

between 

Pb1-xEuxTe barriers, deposited on BaF2 substrates. The 

wires were equipped with side gates for tuning the 

electron concentration. The wire widths W were as 

narrow as 1 mm, and their lengths L = 5 mm. The electron 

mobility in the initial QW was 5 m 2 /Vs, which 

corresponds to the electron mean free path le = 3 mm. 

Therefore, W < le < L , and our structures were in quasiballistic 

regime. The application of negative voltage to 

the gates has led to the total depletion of the wires. The 

measured resistance was then above 10 7 Ohms. 

The low-temperature transport measurements have 

shown characteristic negative magnetoresistance maxima 

which were almost temperature independent in the range 

Fig. 1: Local magnetoresistance of structure T < 20 K (Fig. 1). We assign it to the suppression of the 

shown in the inset. 

electron non-specular backscattering by the wire 

boundaries [6]. 

Nonlocal resistance measurements have been performed in order to search for the signatures of the SHE and 

the inverse SHE [3, 4]. The obtained signal at B = 0 is at least one order of magnitude larger than the value 

expected from the classical van der Pauw formula. However, it is suppressed by the magnetic field with a 

dependence distinctly correlated with the local magnetoresistance. This suggests that the nonlocal resistance may 

be related to non-specular boundary scattering in our wires. 

Acknowledgments: This work was supported by Ministry of Science (Poland) under Grant 

No. 1247/B/H03/2008/35 and under Iuventus Plus grant No. IP2010 006070. 

References 

[1] Markus König et al., Science 318, 766 - 770 (2007). 

[2] Andreas Roth et al., Science 325, 294 - 297 (2009). 

[3] C. Brune et al., Nature Physics 6, 448 - 454 (2010). 

[4] E. M. Hankiewicz et al., Phys. Rev. B 70, 241301 (2004). 

[5] G. Grabecki et al., Phys. Rev. B 72, 125332 (2005). 

[6] C. W. J Beenakker and H. van Houten, Cond-Mat/0412664 (2004). 

39

MoP2 _______________________________________________________________ 


Optical transitions in PbTe/CdTe quantum wells grown by molecular beam 

epitaxy on GaAs (001) and BaF2 (111) substrates 

M. Szot,* L. Kowalczyk, E. Smajek, B. Taliashvili, P. Dziawa, W. Knoff, A. Reszka, 

V. Domukhovski, E. Łusakowska, P. Dłu ewski, M. Wiater, T. Wojtowicz, T. Story, 

M. Bukała, R. Buczko, P. Kacman 

Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland 

IV-VI narrow band gap semiconductors PbTe, PbSe, and PbS constitute materials system 

alternative to III-V semiconductors in the area of mid-infrared lasers and detectors. The 

attractiveness of PbTe/CdTe heterosystem results, inter alia, from a very strong confinement 

of electrons in PbTe caused by large difference in the energy gaps of these semiconductors 

( Eg=1.2 eV at 300 K) and from low Auger recombination rate in PbTe. Additionally, PbTe 

and CdTe exhibit excellent matching of their lattice parameters at room temperature, even 

tough they crystallize in different cubic lattices: zinc blende (a0=6.48 Å) for CdTe and rock 

salt (a0=6.46 Å) for PbTe. Such features are strongly desirable for efficient optoelectronic 

devices operating at room temperature. In this paper, we undertake experimental and 

theoretical studies of ground-state photoluminescence (PL) from PbTe/CdTe quantum wells 

grown along different crystal directions by molecular beam epitaxy (MBE). 

The PbTe/CdTe QWs were grown by the MBE on (001) oriented GaAs and (111) oriented 

BaF2 substrates with thick (1÷4 µm) high quality CdTe buffer layers. The structural quality of 

the heterostructures was examined by x-ray diffraction (XRD) and cross-sectional TEM and 

SEM electron microscopy techniques. The PbTe/CdTe heterostructures with the best crystal 

quality were obtained for the growth at low temperatures (about 260 °C). The XRD rocking 

curve width parameter below 200 arcsec was found for both PbTe and CdTe. For multiple- 

QWs diffraction satellites up 7 th order were observed. The single- and multiple-QWs (3 

repetitions of a basic PbTe/CdTe bilyer) were grown with the thicknesses of PbTe quantum 

wells varying from 4 to 20 nm and 60 nm thick CdTe barriers. 

The optical properties of the heterostructures were examined by the PL measurements using 

1064 nm line of YAG:Nd pulsed laser for excitation. For both (001) and (111) PbTe QWs we 

observed relatively narrow and strong PL which we attribute to the ground-state transitions in 

the PbTe well. The PL energy at T=4 K shifts from 310 meV to 460 meV for (001) PbTe 

QWs with thickness varying from 20 nm to 4 nm, respectively. For a given quantum well 

thickness of 12 nm, the PL energy observed for (111) PbTe QW grown on BaF2 is about 70 

meV lower than for (001) PbTe well. The observed blue shift of the PL line is in good 

agreement with our theoretical analysis of the influence of quantum size effect on the groundstate 

electronic transitions in the PbTe wells. Both studied growth directions were considered 

theoretically. Our calculations were performed within two methods: tight-binding and 

effective mass approximation. The dependence on band offsets in the conduction and valence 

band in the type-I band alignment at the PbTe/CdTe interface was studied. The strong 

effective mass anisotropy and strain induced change of the band gap in PbTe were taken into 

account. The latter effect results from the large difference between PbTe and CdTe 

temperature expansion coefficients. 

This work was partially supported by the European Union within the European Regional 

Development Fund, through the Innovative Economy grant (POIG.01.01.02-00-108/09). 

40

40th _______________________________________________________________ 


Properties of three-dimensional topological insulators 

studied by microwave resonance spectroscopy 

A. Wolos, 1,2 A. Drabinska, 1 M. Kaminska, 1 G. Strzelecka, 3 A. Hruban, 3 A. Materna, 3 

M. Piersa, 3 Z. Wilamowski 2 

1 Faculty of Physics, University of Warsaw, ul Hoza 69, 00-681 Warsaw, Poland. 

2 Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, 

Poland. 

3 Institute of Electronic Materials Technology, ul. Wolczynska 133, 01-919 Warsaw, Poland. 

Bismuth selenide and telluride, as well as other related materials have been recently 

proposed as three-dimensional topological insulators with a single Dirac cone on the surface 

[1]. This class of materials is predicted to show an insulating bulk gap together with gapless 

surface states. Occurrence of the topological surface states has been confirmed by angleresolved 

photoemission spectroscopy [2]. There are, however, only a few reports in literature 

concerning experimental observation of electric transport in the conducting surface, owing to 

large number of bulk carriers (either electrons or holes) originating from crystal defects. In 

order to override presence of highly conductive bulk states shading electric properties of the 

surface, we propose to apply a contactless method basing on a standard electron spin 

resonance (ESR) spectrometery. 

In this communication we discuss results of microwave resonance experiments 

performed on Bi2Te3, Bi2Se3, and Bi2Te2Se crystals grown by vertical Bridgman method in 

Institute of Electronic Materials Technology, Warsaw. The experiment was performed using 

Bruker ELEXSYS E580 spectrometer operating in X- and Q-bands. Semiconducting samples 

placed in a cavity of a standard ESR spectrometer show, in addition to spin resonance spectra, 

also spectral features related to sample conductivity. Using this technique, we have earlier 

investigated Shubnikov-de Haas oscillations, cyclotron resonance or coupled plasmoncyclotron 

resonance in two dimensional electron gas (2DEG) in GaN-based heterostructures 

[3] and in Si-based quantum wells. 

First results obtained for bismuth selenide and telluride samples show a broad 

resonance line dependent only on the component of the external magnetic field perpendicular 

to the sample plane. This feature is characteristic for the cyclotron-related resonances in two 

dimensional electron gas. The relation of the observed resonance line to the topological 

surface states, together with parameters of the 2DEG (concentration and mobility) derived 

from the resonance will be discussed. 

[1] H. Zhang et al. Nature Phys. 5, 438 (2009). 

[2] Y. Xia et al. Nature Phys. 5, 398 (2009). 

[3] A. Wolos et al. Phys. Rev. B 76, 045301 (2007). 

41

MoP4 _______________________________________________________________ 


Analysis of Optical Properties and Pressure Dependence of the Energy Gap of 

ZnO Layers, Bulk and Nano-Powders 

A. Duzynska 1,* , A. Kaminska 1 , H.Teisseyre 1,2 , E. Przezdziecka 1 , D. Dobosz 1 , 

Z.R. Zytkiewicz 1 , A. Kozanecki 1 , J. D. Fidelus 1,2 , A. Durygin 3 , V. Drozd 3 , R. Hrubiak 3 , 

A. Suchocki 1,4 

1 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland 

2 Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw, Poland 

3 CeSMEC, Florida International University, University Park, Miami, FL 33199, USA 

4 Institute of Physics, University of Bydgoszcz, Weyssenhoffa 11, 85-072, Bydgoszcz, Poland 

* Corresponding author: A. Duzynska, e-mail address duzyn@ifpan.edu.pl 

Nowadays zinc oxide (ZnO) is a promising wide-band-gap semiconductor for 

optoelectronic applications, especially in the blue and ultraviolet spectral ranges. An important 

factor affecting mechanical, electric and optical properties of ZnO are methods/conditions of 

growth as well as its crystal form. 

In this project we have studied pressure dependence of the near band gap 

photoluminescence (using the diamond anvil cell technique) of several various samples: 

- two zinc oxide thin layers grown by plasma-assisted molecular beam epitaxy (PA-MBE) on 

sapphire substrates (thickness of the layers: 1µm and 200 nm), 

- bulk ZnO crystal grown by vapor-phase deposition during industrial process of production of 

zinc white, 

- two samples of hexagonal ZnO nano-powders (size of crystallite: 1µm and 65 nm) grown by 

plasma technique. 

We also investigated the stability and the volume behaviour under hydrostatic pressure by 

X-ray powder-diffraction of bulk crystal using synchrotron radiation. The values the bulk moduli 

(B0), and their pressure derivative (B0’), before and after phase transition from wurtzite (B4) to 

rock salt (B1) structure were obtained from these measurements. We found that for wurtzite 

structure B0 is equal to (156 ± 13) GPa and for rock salt phase B0 = (180 ± 59) GPa. In zinc oxide 

the B4-B1 transition has been earlier reported at ~ 10 GPa. However, the change of nanoscale 

grain size has a huge influence on the characteristic of phase transition. We supposed that in the 

case of nano-powders a tetragonal intermediate (iT) appears at the B4/B1 interface and a 

hexagonal intermediate (iH) is also showed as an effect of axial compression [1]. These results 

are visible in our experimental data of pressure dependence of the energy gap EG (≈ EPL), 

especially for nano-powder with 65 nm crystallite size. Moreover experimental band gap 

pressure coefficients for bulk crystal and films grown on sapphire are about 20 meV/GPa, but for 

nano-powders are lower, about 15 meV/GPa. This effect will be also discussed. 

The photoluminescence is quenched at about 10 GPa for ZnO bulk materials as results of 

transition from direct to indirect gap in the rock salt structure. Nonetheless for smaller size nanopowder 

the photoluminescence vanishes at 20 GPa. The origin of this phenomenon will be 

analysed in this work. 

References: 

1. S. E. Boulfelfel and S. Leoni, Phys. Rev. B. 78, 125204 (2008). 

Acknowledgement: This work was partly supported by the European Union within European Regional Development 

Fund, through the Innovative Economy grants (POIG.01.01.02-00-008/0 and POIG.01.01.02-00-108/2009/2) and 

the project no N N202 010134 of Polish Ministry of Science and Higher Education. 

42

40th _______________________________________________________________ 


Defect structure of two-dimensional Wigner crystals 

A. Radzvilavičius and E. Anisimovas 

Department of Theoretical Physics, Vilnius University, Saul˙etekio al. 9-III, LT-10222 

Vilnius, Lithuania 

As the density and temperature of the electron gas is lowered beyond a certain critical 

value, the potential Coulomb energy dominates the kinetic energy and particles tend to 

crystallize. The lowest energy structure of a two-dimensional system thus corresponds to 

the perfect hexagonal Wigner lattice [1]. Finite-size clusters, however, are usually formed 

due to the presence of an external confinement. In many experimental realizations, such 

structures are trapped by a symmetric parabolic potential; these include, but are not 

limited to, micro-metric charged spheres in low-temperature dusty plasmas and electrons 

in semiconductor quantum dots [2]. The structural properties of finite two-dimensional 

Wigner clusters strongly depend on the system size and energetic state. 

In the present contribution, we report the results of 

the numerical Monte Carlo and minima hopping [3] experiments, 

and analyze the structural properties of twodimensional 

Wigner clusters, consisting of classical point 

charges, confined by an external parabolic potential trap. 

Systems of up to N = 1000 particles are considered. 

Thenumberofmetastableconfigurations,corresponding 

to the local minima of the potential energy, grows 

very rapidly with the number of particles. Structurally 

different states are realized with different probabilities. 

By analyzing the number and probabilities of metastable 

configurations we conclude that the configurational uncertainty 

(entropy), grows faster than exponentially – as 

the logarithm of the factorial of the number of particles 

N [4]. 

Small crystals exhibit near-circular symmetry – shell 

structure, induced by the external confinement. Ground 

Figure 1: The triangulated 

structure and defects of 600particle 

Wigner cluster. 

states of larger clusters correspond to a few circular shells at the exterior and an ordered 

hexagonal core. Due to the necessity to satisfy Euler’s theorem and to lower strain energy 

of the lattice, the presence of intrinsic topological defects is unavoidable; these are mainly 

located in the transition region between the circular surface and ordered interior, at the 

six corners of a near-perfect hexagon (figure 1). The number of defective vertices in 

six defect groups grows non-uniformly with the system size. A few distinct species of 

defects are distinguished: disclinations, dislocations, lengthy grain boundaries, unique 

triangular vacancies and interstitial sites. Large pentagonal rosette defects (see figure) 

are also observed in large clusters. As the energy of the metastable state grows, the 

orientational symmetry of the crystal is lost. Long grain boundaries in the interior, large 

numberofdislocationsandnear-surfacecomplexestendtoappearinthehighlymetastable 

configurations. 

[1] E. Wigner, Phys. Rev. 46, 1002 (1934), 

[2] A. V. Filinov, M. Bonitz and Yu. E. Lozovik, Phys. Rev. Lett. 86, 3851 (2001), 

[3] S. Goedecker, J. Chem. Phys. 120, 9911 (2004), 

[4] A. Radzvilavičius and E. Anisimovas, J. Phys.: Condens. Matter 23, 075302 (2011). 

43

MoP6 _______________________________________________________________ 


Gauge invariant computational scheme for heterostructures in magnetic field 

Anna Korbecka and Jacek A. Majewski 

Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, 

ul. Hoża 69 PL-00-681, Poland 

Multiband k·p models together with the envelope function theory have become a standard 

approach for studies of the electronic structure of not only bulk semiconductors but also their 

heterostructures, other low-dimensional forms, and semiconductors in the translational symmetry 

breaking magnetic field. This continuum scheme proved to be very useful for modeling of 

semiconductor nanostructures, albeit not free from flaws. In applications of this method for 

structures where the translational symmetry is broken, the corresponding component of the wave 

vector is substituted by differential operator. Together with the fact that parameters of the k·p 

Hamiltonian are position dependent, it leads to the situation where the operators representing 

individual components of the total matrix operator are not hermitian. Therefore, these operators are 

modified (so-called ‘symmetrization’ is performed) to acquire hermitian form. It solves some of the 

severe problems, however the ‘symmetrization’ procedure is not unique and very often leads to 

unphysical spurious solutions [1] and nonphysical outcomes for the heavy-hole subbands [2]. The 

problem has been disputed hotly for a long time in semiconductor physics without a final solution 

on the horizon. In the meantime, the new approach has emerged that is based on the so-called Burt’s 

exact envelope function theory [3] and formulates the whole operator matrix in a proper form 

instead of ‘symmetrizing’ its individual components [4], i.e., the whole matrix of operators is 

hermitian, however, its individual operator components are not. This procedure of B.A. Foreman is 

not plagued by spurious solutions problem and gives in most cases physically reasonable results, 

which can be, however, quite different from ones obtained within the standard approach. In 

addition, it has been recently proved [2] that the Foreman’s scheme is the only one that guarantees 

the gauge invariance of the k·p Hamiltonian for semiconductor low-dimensional structures in the 

constant magnetic field. 

We have implemented Foreman’s theory for low dimensional semiconducting systems in 

magnetic field into nextnano 3 simulation package [5] together with the magnetic p-d exchange 

interaction [6] and interface corrections for systems without mirror symmetry (e.g., no-common 

atom systems like InAs/GaSb). The Hamiltonian has been solved on discrete lattice. This allows us 

for reliable studies of the Landau level formation in the valence bands in non-magnetic 

heterostructures (GaAs/AlGaAs, InGaAs/GaAs, InAs/GaSb) and also heterostructures with 

modulated magnetization (such as (Ga,Mn)As/AlGaAs and (Ga,Mn)Sb/InAs). The scheme deals 

also with the doped structures, by including the electrostatic potential obtained from the Poisson’s 

equation self-consistently into Foreman’s k·p Hamiltonian. 

In particular, we have computed the electronic structure of GaAs/Al0.33Ga0.67As [001] and 

[311] heterostructures in the magnetic field. The obtained results help to interpret experiments on gfactor 

in 2D-hole gases [6] and the intrinsic photo-induced anomalous Hall effect [7]. 

[1] E. P. Pokalitov, V. A. Fonoberov, V. M. Fomin, and J.T. Devreese, Phys. Rev. B. 64, 245328 (2001). 

[2] T. Andlauer, R. Morsch, P. Vogl, Phys. Rev. B. 78, 075317 (2008). 

[3] M. G. Burt, J. Phys. Condens. Matter 4, 6651 (1992). 

[4] B. A. Foreman, Phys. Rev. B. 48, 4964 (1993); ibid. 56, R12 748 (1997). 

[5] http://www.nextnano.de 

[6] D.A. Vasyukov, A.S.Plaut, M.Henini, Physica E 42, 964 (2010). 

[7] D.A. Vasyukov, A.S.Plaut, M.Henini, L.N.Pfeiffer, K.W.West, C.A.Nicoll, I.Farrer, and D.A. Ritchie, 

Physica E 42, 940 (2010). 

44

40th _______________________________________________________________ 


Modeling PbTe-based low dimensional structures 

M. Bukała 1 , P. Sankowski 2 , R. Buczko 1 and P. Kacman 1 

1 Institute of Physics, Polish Academy of Sciences, Warsaw 02-668, Poland 

2 Institute of Informatics, University of Warsaw, Warsaw 02-097, Poland 

We present a theoretical study of various PbTe low dimensional structures. First, we 

consider rock-salt PbTe inclusions in zinc-blende CdTe matrix as well as of zinc-blende CdTe 

nano-clusters in rock-salt PbTe matrix i.e. structures with possibly improved thermoelectric 

properties. Next, we model PbTe-based 2D heterostructures, in which quantum spin-Hall 

phase is expected. For these purposes a tight-binding parameterisation for PbTe has been 

obtained, which, in contrast to all available in literature parameterisations, leads not only to 

proper values of the energy gaps but also to adequate effective masses in the valence and 

conduction bands. Our tight-binding model includes the sp3 atomic orbitals with spin-orbit 

interactions and accounts for the nearest neighbour and next near neighbour interactions. We 

have checked on 2D PbTe/CdTe heterostructures that such tight-binding description and the 

effective mass approach lead to similar energy structures. 

The aim of the former research is to show how introducing nanostructures of different 

size and shape changes the electron density of states near the Fermi level and thus can be used 

to optimize the thermoelectric power Seeback coefficient. We have considered the Fermi level 

situated near the top of the valence band (in p-type) as well as at the bottom of the conduction 

band (in n-type). We have studied structural and electronic properties of PbTe quantum wires 

in the CdTe matrix, and CdTe anti-wires and CdTe anti-dots in the PbTe matrix. For structures 

with less than 500 atoms in the unit cell, all atomic positions in the model nanostructures, in 

particular at the interfaces, have been calculated using first principles methods with relaxation 

and re-bonding allowed. The obtained relaxed atomic positions have been further used in the 

calculations of electron density of states of the studied structures, which are performed within 

the tight-binding approximation. In larger structures the relaxation has not been taken into 

account. 

Our calculations show that all kinds of inclusions can lead to shape and size dependent 

changes of the density of states at the Fermi level. Thus, the electronic contribution to the 

Seebeck coefficient can be optimized by changing the shape, size, density as well as the 

spatial arrangement of the inclusions. 

The same tight-binding model, supported by effective mass approach, have been used to 

study the PbTe-based 2D heterostructures. In particular, it has been shown that states related 

to the interfaces can appear in PbSnTe/PbTe structure, in which the Sn content leads to band 

inversion. By changing the Sn content and the diameter of the heterostructure, we are looking 

for systems, in which such states may lead to the spin-Hall effect. 

The work was partially supported by the European Union within the European Regional 

Development Fund, through grant Innovative Economy (POIG.01.01.02-00-108/09) 

45

MoP8 _______________________________________________________________ 


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46

40th _______________________________________________________________ 


Atomistic calculation of screened Coulomb interactions in semiconductor 

nanostructures. 

M. Chwastyk, P. T. Różański, and M. Zieliński 

Instytut Fizyki UMK, ul. Grudziądzka 5, 87-100 Toruń, Poland 

Dielectric screening of Coulomb interactions affects optical and electronic properties 

of semiconductor nanostructures including multi-exciton generation rates in colloidal 

nanocrystals [1], excitonic spectra and self-energy corrections in nanopillar or graphene 

quantum dots [2,3]. Using tight-binding approach we compare several methods of accounting 

for dielectric screening in atomistic calculation including semi-classical approximation [4], 

Thomas-Fermi approach [5] and real-space dielectric matrix inversion [6]. We propose an 

efficient method in which dielectric screening can be decomposed into contribution from 

volume and surface-polarization terms, further screened by microscopic Thomas-Fermi like 

contribution. We illustrate our approach by calculating electronic and optical properties of 

several different spherical semiconductor nanocrystals differing in size and composition. We 

compare results obtained with proposed approach and real-space dielectric matrix inversion 

and study role of different approximation used in calculation. We discuss possibility 

generalizing our model for a multi-million atom systems like self-assembled quantum dots. 

[1] Z. Lin, A. Franceschetti, and M.T. Lusk, arXiv:1009.0417 

[2] Y. M. Niquet et al., Phys. Rev. B 73, 165319 (2006). 

[3] D. Guclu, P. Potasz, and P. Hawrylak Phys. Rev. B 82, 155445 (2010). 

[4] A. Franceschetti and M. C. Troparevsky, Phys. Rev. B 72, 165311 (2005). 

[5] S. Lee et al., Phys. Rev. B 63, 195318 (2001). 

[6] F. Trani, D. Ninno, and G. Iadonisi, Phys. Rev. B 76, 085326 (2007). 

47

MoP10 _______________________________________________________________ 


Van der Waals Density Functionals in Materials Science 

Magda Birowska, Karolina Milowska, and Jacek A. Majewski 

Faculty of Physics, University of Warsaw, ul. Hoża 69, 00-681 Warszawa, Poland 

The density functional theory (DFT) has revolutionized materials science making it possible 

to quantitatively predict numerous properties of materials. However, exact in principle, the DFT 

relies on various approximations to the exchange and correlation functionals that are nowadays 

prerequisites for practical implementations of DFT. In spite of a long list of successes, the local 

density approximation (LDA) or generalized gradient approximation (GGA) that are commonly 

used in so-called ab-initio calculations have as well many flaws. One of its weaknesses is rather 

poor description of Van der Waals (VdW) type of bonding in solids. The best example is the 

geometry unit cell geometry of graphite. Whereas the atomic distances in the carbon planes with 

strong covalent bonds are excellently predicted by LDA or GGA, the distances between the 

planes, which are determined by Van der Waals type of interactions, are not. Therefore, recently 

new correlation functionals have emerged that take into account polarization effects and could 

improve the description of Van der Waals forces [1,2]. 

In this communication, we present the results of theoretical studies of various systems with 

considerable role of VdW forces where the new functionals have been employed. The results of 

test studies for graphite are very promising, providing the solution to the long standing problem 

and giving the distance between the carbon layers equal to 3.349 Å (with DRSLL functional [1]) 

or 3.345 Å (with LMKLL one [2]) in excellent agreement with experimental value of 3.36 Å 

(LDA and GGA lead to distances equal to 3.117 Å and 3.425 Å, respectively). However, in the 

studies we focus on graphene single-, bi-, and multi-layers, either free standing or bound in an 

incommensurable way to silicon carbide substrate. We consider also functionalized graphene 

layers. The correct description of the structural and electronic properties of these systems is of 

crucial importance for the quickly developing electronics based on graphene. In our studies of 

materials we have used the numerical package SIESTA with implemented VdW functionals and 

the standard LDA and GGA ones. This facilitates the direct comparison of the material 

properties obtained within both approaches. We find differences in the electronic structures of 

these systems and their energetics. In particular, we find that the potential barriers in these 

systems calculated with VdW functional and standard approaches in many cases differ 

considerably. It is of crucial importance, particularly if one uses atomistic ab initio methods as a 

starting point for multi-scale modeling of materials and determines effective potentials on the 

basis of DFT calculations. 

This paper has been supported by the project “SiCMAT” (POIG.01.03.01-14-155/09-00). 

[1] M. Dion, H. Rydberg,E. Schoder, D. C. Langreth, and B. I. Lundqvist, Phys. Rev. Lett. 92, 

246401 (2004) 

[2] K. Lee, E. Murray, L. Kong, B. I. Lundqvist and D. C. Langreth, arXiv:1003.5255v1 (2010). 

48

40th _______________________________________________________________ 


Hopkinson-Like Effect in Single-Crystalline CdCr2Se4 Semiconductor 

T. Groń 1 , E. Malicka 2 , A.W. Pacyna 3 , H. Duda 1 and J. Krok-Kowalski 1 

1 University of Silesia, Institute of Physics, ul. Uniwersytecka 4, 40-007 Katowice, Poland 

2 University of Silesia, Institute of Chemistry, ul. Szkolna 9, 40-006 Katowice, Poland 

3 The Henryk Niewodniczański Institute of Nuclear Physics, Polish Academy of Sciences, 

ul. Radzikowskiego 152, 31-342 Kraków, Poland 

The magnetization of many compounds shows a peak near the Curie temperature, TC, 

when heating the sample in a fixed (small) magnetic field [1]. This behavior is commonly 

called the Hopkinson effect [2]. The accepted explanation [3] of the Hopkinson effect is based 

only on domain wall motion. This mechanism is obviously inapplicable to the case of singledomain 

particles. However, a thermomagnetic effect which is quite similar to the Hopkinson 

effect has been experimentally observed in most of the amorphous magnetic materials as well 

as in some spin glasses where the existence of multi-domain particles is questionable or even 

practically impossible [2]. In Nd2Fe14B-type ribbons the existence of a maximum in the 

thermomagnetic curves of thermally demagnetized samples in low fields was connected with 

the processes of irreversible rotation of magnetic moments of non-interacting uniaxial single 

domain particles according to the Stoner-Wohlfarth model [2,4]. 

Magnetization, ac and dc magnetic susceptibility of the p-type CdCr2Se4 semiconductor 

[5] were measured in the zero-field-cooled mode using a Lake Shore 7225 dc 

magnetometer/ac susceptometer at 4.3 K and in applied external magnetic fields up to 60 kOe, 

and a Faraday type Cahn RG automatic electrobalance in the temperature range 4.5-400 K and 

' 

" 

at 1 kOe, respectively. The in-phase c ( T) 

and out-of-phase c ( T) 

components of the ac 

1 

fundamental susceptibility were recorded in the temperature range 4.5-160 K using an 

oscillating field Hac = 1 Oe with frequency of 120 Hz for external magnetic fields Hdc = 0, 100 

Oe, 200 Oe, 450 Oe and 1 kOe. The signals of the second (c2) and third (c3) harmonics were 

detected at the same temperature range, for the same amplitude and frequency as the ac c1 

measurements without an external static magnetic field. 

The dc magnetic measurements showed ferromagnetic order with a Curie temperature 

TC = 130 K and a saturation magnetization of 5.91 µB/f.u. at 4.5 K and at 60 kOe. The ac 

' 

magnetic measurements revealed a spectacular peak at 450 Oe and 1 kOe in the c 1( 

T) 

curve 

near TC, similar to the Hopkinson peak. The increasing dc magnetic field suppresses the 

' 

magnetic susceptibility intensity of c ( T) 

and slightly shifts the Hopkinson peak to higher 

1 

" 

temperatures. A small and positive value of c1( T) 

below TC indicating a small energy loss 

correlates rather with strong spin fluctuations than with spin rearrangement processes. This is 

consistent with zero values of second and third harmonic ac susceptibility in the temperature 

range of 4.5-160 K, suggesting the lack of short-range magnetic interactions. One can 

conclude that the peaks in the thermomagnetic curves at 450 Oe and 1 kOe can be 

qualitatively explained with the aid of the Hopkinson-like effect. 

This work is partly founded from science Grant No. N N204 145938. 

[1] J. Hopkinson, Proc. R. Soc. London 48, 1 (1890). 

[2] O. Popov, and M. Mikhov, J. Magn. Magn. Mater. 75, 135 (1988). 

[3] M. Kersten, Z. Angew. Phys. 8, 313 (1956). 

[4] E.C. Stoner, and E.P. Wohlfarth, Phil. Trans. R. Soc. A 240, 599 (1948). 

[5] H.W. Lehmann, Phys. Rev. 163, 488 (1967). 

49 

1

MoP12 _______________________________________________________________ 


Optical and structural characterization of zinc oxide 

nanostructures obtained by Atomic Layer Deposition method 

Ł. Wachnicki 1 , B. S. Witkowski 1 , S. Gierałtowska 1 , E. Janik 1 , M. Godlewski 1,2 , 

E. Guziewicz 1 

1 Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, 

Poland 

2 Cardinal Stefan Wyszynski University, College of Science, Department of Mathematics and 

Natural Sciences, Warszawa, Poland 

Zinc oxide has been extensively investigated in the past few years mainly 

because of a large variety of potential applications. For example, it can be used 

in light-emitting diodes and transistors, as gas sensors, and transparent 

conductive oxide in solar cells. 

Among many applications, ZnO is also a prospective material for sensor 

technology, where developed surface morphology is very important. In this 

work we present growth of ZnO nanostructures using ALD. As a substrate we 

used gallium arsenide with gold eutectic mixture prepared on the surface at 

600°C. To obtain eutectic solution we spread gold thin film on a GaAs substrate 

and then annealed the sample in a nitrogen gas flow. Au-Ga droplets where 

formed in this way. The so-prepared substrate was used for growth of ZnO 

nanostructures in the ALD system. We applied deionized water and zinc 

chloride as an oxygen and zinc precursors, respectively. The eutectic mixture 

plays a role of a catalyst for the ZnO nanostructures growth. Au-Ga droplets 

flow on the front of growth forcing the growth of ZnO nanostructures. Optical 

and structural characterization was investigated by photoluminescence, scanning 

electron microscope (SEM) and atomic force microscope (AFM). SEM images 

show ZnO nanorods in a form of crystallites of up to 1 m length and 100 nm 

diameters. It is the first demonstration of ZnO nanostructures growth by ALD 

using VLS (vapour-liquid-solid) approach. 

The research was supported by the European Union within European Regional 

Development Fund, through grant Innovative Economy (POIG.01.01.02-00- 

008/08). 

50

40th _______________________________________________________________ 


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MoP14 _______________________________________________________________ 


Photoluminescence and chromaticity properties of ZnO nanopowders 

obtained by a microwave solwothermal method 

E. Wolska 1 , D. Sibera 2 , B.S. Witkowski 1 , S.A. Yatsunenko 1 , I. Pełech 2 , 

U. Narkiewicz 2 , M. Godlewski 1,3 

1 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 

02-668 Warsaw, Poland 

2 Institute of Chemical and Environment Engineering, West Pomeranian University of 

Technology, K. Puławskiego 10, 70-322 Szczecin, Poland. 

3 Dept. of Mathematics and Natural Sciences College of Science, 

Cardinal S. Wyszy ski University, Dewajtis 5, 01-815 Warsaw, Poland 

ZnO is one of the most intensively studied wide band gap semiconducting material. 

Different applications of ZnO in transparent electronics, optoelectronics, photovoltaics 

and spintronics were demonstrated recently, which explains the increasing interest in this 

material. Moreover, new applications in medicine and biology are predicted. It is claimed 

that ZnO nanopowders can be used as luminescence markers for such applications. 

Luminescence markers are promising materials to be used for early recognition of many 

of diseases, including cancer. 

In the present work we discuss growth and properties of ZnO nanopowders obtained by a 

microwave solvothermal method. We compare properties of nanopowders obtained by 

two methods. In the first process as a zinc precursor we used zinc nitrate hexahydrate 

(Zn(NO3)2 6H2O) dissolved in distilled water. In the second process we used zinc nitrate 

hexahydrate and ethanol. For each of these two processes we performed growth at five 

different values of pressure in the microwave reactor during the solvothermal synthesis. 

The so-obtained powders were studied as-grown or after annealing at 750 o C in the air 

atmosphere. 

Each type of the samples were characterized with photoluminescence, 

cathodoluminescence and their size was determined from SEM and XRD investigations. 

The growth processes were optimized to obtain the brightness light emission and, in some 

cases, the best chromaticity. The latter study was motivated by possibility of white color 

emission of ZnO upon UV excitation. 

We discuss relations between synthesis parameters in the solvothermal microwave 

processes and optical properties of the samples obtained. 

The research was partially supported by the European Union within European Regional 

Development Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08). 

52

40th _______________________________________________________________ 


Technology and testing the mechanical properties of the 

InGaP/GaAs/InGaP microcantilevers 

Tomáš Ščepka, Dagmar Gregušová, Róbert Kúdela, Štefan Gaži and Vladimír 

Cambel 

Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, SK- 

84104 Bratislava, Slovakia 

Microcantilevers are at the heart of atomic force microscopes and also perspective for 

future chemical and biological sensing applications. Most of the commercially produced 

cantilevers are made of silicon or silicon nitride. However, microcantilever probes based on 

III-V semiconductor materials and their heterostructures can be equipped with novel 

functionalities through the incorporation of electronic and opto-electronic devices designed 

directly on them. 

GaAs is the most used III-V material for cantilever probe development thanks to its 

optoelectronic properties, high mobility of electrons, sufficient mechanical properties and 

high piezoresistivity (values higher than those of silicon) [1]. Application of mature 

deposition methods, such as metal organic chemical vapor deposition, allows for the 

formation of sandwich layers whose thickness can be defined with extreme precision. 

This work is a first step towards sensors with improved sensitivity and integrability. 

We focus on the fabrication and initial mechanical testing of microcantilevers based on an 

InGaP/GaAs/InGaP heterostructure (Fig. 1.). The heterostructure consists of a GaAs layer, 

that determined the cantilever thickness. The layer is embedded between two InGaP etch-stop 

layers [2]. All layers are lattice matched to a thinned semi-insulating GaAs (100) substrate. 

The front-side patterning was accomplished using optical photolithography, Ar ion milling of 

InGaP layer, and wet chemical etching of GaAs. The substrate was at first thinned to ~250 µm 

and then cantilevers were released via back-side bulk micromachining in two solutions. The 

1H2SO4:8H2O2:1H2O mixture was used as a fast etchant 

which was followed by a finer 1H3PO4:2H2O2:8H2O 

etchant. The experimental cantilevers presented here 

were designed as simple rectangles, nominally 100-300 

µm long and 35-65 µm wide, with a thickness of 0.1, 0.2, 

0.5, 1, and 2 µm. We have investigated the influence of 

geometrical dimensions, especially thickness of GaAs 

layer, on the fabrication process and mechanical 

properties of the cantilevers. To determine the resonance 

frequencies, a detection system of an Atomic Force 

Microscope (NT-MDT NTEGRA) was used. The 

measured resonance frequencies of the cantilevers 

correspond with theoretical values. 

This work is the result of the ESF project implementation, CENTE - 2 nd stage, ITMS code 

26240120019, supported by the R&D Operational Program funded by the ERDF. 

[1] K. Hjort et al., J. Micromech. Microeng. 4, 1-13 (1994). 

[2] D. Gregušová et al., J. Micromech. Microeng. 20, 097001 (2010). 

53 

Figure 1. SEM micrograph of 

fabricated microcantilever.

MoP16 _______________________________________________________________ 


ZnO thin films of different crystalline structures grown on Si (100) 

substrates by reactive DC sputter deposition 

Michał A. Borysiewicz 1 , El bieta Dynowska 1,2 , Valery Kolkovsky 2 , Jan Dyczewski 2 , 

Eliana Kami ska 1 , Anna Piotrowska 1 

1 Institute of Electron Technology, Al. Lotników 32/46, 02-668 Warsaw, Poland 

2 Institute of Physics, Polish Acad. of Sci., Al. Lotników 32/46, 02-668 Warsaw, Poland 

ZnO is considered an advantageous material in the transparent electronics, 

optoelectronics and photovoltaics due to its wide band-gap of 3.37 eV and high exciton 

binding energy of about 60 meV. Most research on ZnO thin films is performed on layers 

deposited on sapphire substrates. The sapphire has the advantage of having a crystalline 

structure matching that of the ZnO, but also a disadvantage of a large lattice mismatch of 

~18%. Therefore, to grow high-quality ZnO thin films on sapphire substrates, buffer layers 

have to be introduced [1-3]. On the other hand, in order to enable the integration of electronic 

and optoelectronic elements on one chip and take advantage of the high quality, large wafer 

sizes and low price, ZnO growth on silicon (100) substrates should be studied, regardless of 

the lattice mismatch to ZnO. 

This work reports on the structure of thin ZnO films on Si (100) substrates deposited 

using room-temperature reactive DC sputtering from a Zn target in an Ar-O2 mixture. Films 

grown in several deposition processes are compared. The power fed to the Zn target was kept 

at 75 W and the total gas pressures and amounts of oxygen in the gas mixture were changed 

between the processes. The structure of the films was studied by means of X-ray diffraction in 

the -2 geometry and scanning electron microscopy of the surface as well as the crosssections. 

The stoichiometry was estimated using Rutherford backscattering spectrometry. 

Transport properties were determined through Hall effect measurements. The 

characterisations were carried out after deposition and after subsequent 15 minutes-long 

annealing processes in an RTP furnace in O2 flow at 400 o C, 600 o C and 800 o C. We found, that 

by varying the parameters of the growth accordingly, films with very different structures 

could be produced. In particular, growth in oxygen-poor conditions resulted in porous 

polycrystalline structures (Fig. 1) potentially suited for applications in chemical sensors or 

dye-sensitized solar cells and growth in oxygen-rich conditions led to the formation of dense 

columnar films (Fig. 2) which may be applied in LEDs. 

This study was partially supported by the European Union within European Regional 

Development Fund, through grant Innovative Economy (POIG.01.03.01-00-159/08, 

"InTechFun"). 

Fig. 1. Fig. 2. 

[1] B. Pecz et al., J. Appl. Phys. 100, 103506 (2006) 

[2] M.W. Cho et al., Semicond. Sci. Technol. 20, S13–S21 (2005) 

[3] M.A. Borysiewicz et al., Acta Phys. Pol. A 119, 333 (2011) 

54

40th _______________________________________________________________ 


Comparison of the valence band of amorphous and crystalline 

GeTe and (Ge,Mn)Te layers 

W. Knoff 1 , M.A. Pietrzyk 1 , B.A. Orłowski 1 , B. Taliashvili 1 , T. Story 1 , R.L. Johnson 2 

1 Institute of Physics, PAS, Al. Lotników 32/46, 02-668 Warsaw, Poland 

2 Institute of Experimental Physics, University of Hamburg, Luruper Chaussee 149, 

D-22761 Hamburg, Germany 

(Ge,Mn)Te belongs to the IV-VI family of diluted magnetic semiconductors and attracts 

considerable attention due to its ferroelectricity and carrier-induced ferromagnetism governed 

by the RKKY indirect exchange mechanism. GeTe is also known as a phase change material 

exhibiting at the nanosecond scale a transformation from an amorphous to a polycrystalline 

phase, accompanied by insulator to metal transition. In (Ge,Mn)Te layers this structural 

transformation results also in paramagnet to ferromagnet transition. The aim of this work is to 

compare electronic structure of amorphous (a-) and crystalline (c-) GeTe and Ge0.9Mn0.1Te 

semiconductors using resonant photoemission spectroscopy (RPES) method. 

GeTe and (Ge,Mn)Te layers were grown on BaF2 (111) substrates by molecular beam epitaxy 

technique using effusion cells with GeTe, Mn, and Te2. For the growth of amorphous and 

crystalline GeTe and (Ge,Mn)Te layers, the substrate temperature was kept at room 

temperature and at T=250 0 C, respectively. Mn content in the layers was determined by energy 

dispersive X-ray fluorescence analysis. No evidence of crystalline phases was found in 

a-GeTe and a-(Ge,Mn)Te layers by X-ray diffraction (XRD) measurements. GeTe and 

(Ge,Mn)Te layers deposited at higher temperature (T=250 0 C) grow epitaxially and are 

monocrystalline with [111] growth direction. For GeTe and (Ge,Mn)Te layers the 

photoemission spectra were measured in the photon energy range 45-60 eV. The three-peak 

structure related to 4p and 5p Te orbitals (about 2.6 eV), Ge 4s orbitals (7.6 eV), and Te 5s 

orbitals (12 eV) was experimentally observed in the valence band of both c-GeTe and a-GeTe 

[1-3]. The spectra obtained for c-(Ge,Mn)Te and a-(Ge,Mn)Te in the energy range 

corresponding to the transition from Mn 3p to Mn 3d states reveal the same structure of peaks 

and Mn 3d orbitals contribution at 4 eV. 

Intensity (arb.u.) 

a) 

c-GeTe 

a-GeTe 

hυ = 50 eV 

0 5 10 15 

Binding Energy (eV) 

0 5 10 15 20 25 

Binding Energy (eV) 

Fig.1 The valence band photoemission spectra of amorphous and crystalline GeTe (figure a) and (Ge,Mn)Te 

(figure b). The spectrum of (Ge,Mn)Te was measured at the energy corresponding to the Mn 3p-3d threshold. 

[1] N.J. Shevchik, J. Tejada, W.W. Langer, M. Cardona, Phys. Rev. Lett., 30 659 (1973). 

[2] B.J. Kowalski, M.A. Pietrzyk, W. Knoff, et al., Physics Procedia 3 1357 (2010). 

[3] M.A. Pietrzyk, B.J. Kowalski, B.A. Orłowski, et al., Acta Phys. Pol. A 112, 275 (2007). 

c-(Ge,Mn)Te 

a-(Ge,Mn)Te 

hν=51 eV 

This work was partially supported by the EC Network SemiSpinNet (PITN-GA-2008-215368). 

55 

Intensity (arb.u.) 

b)

MoP18 _______________________________________________________________ 


Local Structure Study of GaAs:Te Using Te K-edge X-ray Absorption Fine 

Structure. 

A. Pietnoczka 1 , R. Bacewicz 1 , T. Słupi ski 2 , S. H. Wei 3 , M. Jie 3 , J. Antonowicz 1 , 

T. Drobiazg 1 

1 Faculty of Physics, Warsaw University of Technology, ul. Koszykowa 75, 00-662 Warsaw, 

Poland 

2 Faculty of Physics, University of Warsaw, Ho a 69, Warsaw 00-681, Poland 

3 NREL, 1617 Cole Blvd., Golden, CO 80401, USA 

The annealing of heavily doped GaAs:Te can significantly change the value of the free 

electron concentration in a reversible manner. These changes of electrical properties are 

accompanied by the structural changes of GaAs:Te solid solution.[1] In this contribution we 

present an attempt to determine local changes around Te atoms for different states of the 

GaAs:Te crystals caused by the annealing corresponding to different electron concentrations. 

Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge 

Structure (XANES) techniques have been employed to investigate the local structure around 

tellurium atom and its valence. Tellurium K-edge absorption has been measured in a 

fluorescence method at the X1 beamline in the HASYLAB. The samples were kept at the 

temperature of 80 K in order to minimize the thermal disorder. 

Various models of Te defect complex have been used to fit the data for low 

concentration state: VGa- TeAs complexes [2], TeAs+ TeAs pairs [1], as well as several DX-like 

configurations of tellurium. DX configurations have been calculated using density functional 

theory (DFT). The EXAFS and XANES spectra for different Te location have been simulated 

and compared with the experimental data. Multi-parameter fitting of the EXAFS data 

provided information on the local structure around Te (the bond lengths, the coordination 

numbers and Debye-Waller factor). The charge state of Te has been determined from the 

XANES data. The EXAFS and XANES were useful for ruling out the possibility of existence 

GaTe and Ga2Te3 precipitations. 

The XAFS results have been compared with the studies of structural disorder using the 

X-ray diffuse scattering. 

References: 

[1] T.Słupi ski, E.Zieli ska-Rohozi ska, Thin Solid Films 367, 227 (2000). 

[2] D.T.J. Hurle, J. Appl. Phys. 85, 6957 (1999). 

56

40th _______________________________________________________________ 


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MoP20 _______________________________________________________________ 


Investigation of thermal properties of AlGaAs/GaAs Quantum 

Cascade Lasers by thermoreflectance spectroscopy 

Małgorzata Iwi ska 1,2 , Dorota Pier ci ska 1 , Kamil Pier ci ski 1 , 

Anna Szerling 1 , Piotr Karbownik 1 , Maciej Bugajski 1,2 

1 Institute of Electron Technology, al. Lotników 32/46, 02-668 Warsaw, Poland 

2 Faculty of Physics, WUT, ul. Koszykowa 75, 00-662 Warsaw, Poland 

Abstract 

Quantum Cascade Lasers (QCLs) are semiconductor unipolar devices in 

which intersubband transitions of carriers lead to lasing. The QCL design’s 

characteristic feature is the active regions cascading scheme. The wavelength of 

emitted radiation in QCLs depends mainly on the width and the depth of quantum 

wells and to the less extend on the material. QCLs emit wavelengths within the 

infrared region of the spectrum and which covers most of molecules’ absorption 

bands. This makes them ideal sources for trace gases detection, air pollution 

monitoring, human’s exhaled breath monitoring or biomedical imaging. Most of 

QCL applications require devices operating at room temperature (RT), often in 

CW mode, which is not an easy task to achieve. 

For full exploitation of QCLs application potential understanding of 

thermal management in the devices is necessary. For CW RT operation the active 

region temperature has to be kept under control. Its value depends on such 

parameters as the pulse frequency, the pulse width, device mounting technology 

and the heat sink temperature. The excessive temperature of the active region 

causes escape of the electrons from the upper laser level to continuum states and 

thermal backfilling of the lower laser level, both processes deteriorating device 

performance by lowering the laser gain. 

The AlGaAs/GaAs QCLs investigated in this work are designed and 

fabricated at the Institute of Electron Technology in Warsaw [1]. The aim of the 

study was to determine the main factors influencing temperature rise in QCLs and 

to optimise their thermal properties. The measurements included temperature 

dependence of light current (I-V) characteristics and measurements of temperature 

distributions within devices. The latter were obtained by spatially resolved 

thermoreflectance measurements [2,3], which is the technique allowing for high 

resolution temperature mapping on working devices. 

1. K. Kosiel, M. Bugajski, A. Szerling, J. Kubacka-Traczyk, P. Karbownik, E. Pruszy ska- 

Karbownik, J. Muszalski, A. Łaszcz, P. Romanowski, M. Wasiak, W. Nakwaski, I. 

Makarowa, P. Perlin , Photonics Letters of Poland, vol.1, 16-18, (2009) 

2. M. Bugajski, T. Piwoñski, D. Wawer, T. Ochalski, E. Deichsel, P. Unger, B. Corbett, 

Materials Science in Semiconductor Processing, vol.9, 188-197 (2006) 

D. Wawer, T. J. Ochalski, T. Piwo ski, A. Wójcik-Jedli ska, M. Bugajski, H. Page, phys. 

stat. sol. (a) 202, 1227–1232 (2005) 

58

40th _______________________________________________________________ 


Luminescence properties of Sm 3+ in different phases of TiO2 

P. Łach 1 , M. G. Brik 2 , I. Sildos 2 , A. Kamińska 1 , and A. Suchocki 1,3 

1 

- Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668, Warsaw, 

Poland 

2 

- Institute of Physics, University of Tartu, Riia 142, Tartu 51014, Estonia 

3 

- Institute of Physics, Kazimierz Wielki University, Weyssenhoffa 11, Bydgoszcz 85-072, 

Poland 

Titanium dioxide (TiO2) belongs to the wide-gap (3.0-3.2 eV) semiconductors and it 

has a very good performance as a photocatalyst and an oxygen sensor. Recently, it has been 

considered as a host suitable for doping with rare (RE) ions. In particular, samarium-doped 

titania reveals interesting phenomena like intense host-emission, high sensitivity of the 

emission on the ambient gas and enhanced photocatalytic activity [1]. 

We have carried out studies of the photoluminescence of Sm 3+ -doped TiO2 within the 

temperature range 10 – 300 K in order to show the energy levels of the trivalent impurity ion 

in two different phases of titania. The anatase TiO2 crystallizes in I41/amd space group, in a 

tetragonal structure, the lattice parameters are equal to 3.7850 and 9.5140 Ǻ. The rutile TiO2 

crystallizes in the P42/mnm space group and lattice parameters are equal to 4.593 and 2.959 

Ǻ. In order to obtain crystalline titania powder in both of these two phases our samples were 

annealed: up to 700°C and at 1100 °C for anatase and rutile phases, respectively. Thanks to 

that we have obtained a maximum of Sm emission intensity [2], which depends on the 

ambient around the samples. The best luminescence signals were observed during the 

measurements in the atmospheric oxygen. We have used the over band-gap excitation in both 

cases. The PL intensity of rutile titania was much lower than in the corresponding anatase 

TiO2 at room temperature. In the two cases we have also observed the PL spectra at low 

temperatures. Unfortunately in argon atmosphere our samples have not given any signals. 

An example of PL spectrum of Sm 3+ in TiO2 at room temperature under the band-toband 

excitation of the anatase structure is presented below. 

PL intenity [au] 

0,007 

0,006 

0,005 

0,004 

0,003 

0,002 

0,001 

0,000 

6 H7/2 

6 H5/2 

6 H9/2 

6 H11/2 

500 550 600 650 700 750 

Wavelength [nm] 

Sm 3+ in anatase TiO 2 

λ exc = 325 nm 

T=300K 

In order to check the influence of high pressure on the photoluminescence properties 

of both phases titanium oxide doped with Sm we have used the intra-center excitation (488 

nm) in a diamond anvil-cell at low temperature. Pressure coefficients of the various 

luminescence lines were established. Pressure dependence of the crystals field parameters f 

Sm 3+ ions were calculated on this basis. 

Acknowledgements: This work was partly supported by the European Union within European Regional 

Development Fund, through the Innovative Economy grant POIG.01.01.02-00-108/2009/3 

References: 

[1] M.G. Brik et al., Physica B 405 (2010) 2450-2456 

[2] V. Kiisk et al., J. Phys. D: Appl. Phys. 42 (2009) 125107 

59

MoP22 _______________________________________________________________ 


Investigation of electro-optical properties of 2D macroporous silicon 

structures with surface nanocrystals 

Lyudmila A. Karachevtseva a , Stepan Ya. Kuchmii b , Oleg A. Lytvynenko a , 

Fedor F. Sizov a , Olena J. Stronska a , Alexandr L. Stroyuk b 

a V. Lashkaryov Institute of Semiconductor Physics of NASU, Kyiv, Ukraine 

b L.V. Pisarzhevskii Institute of Physical Chemistry of NASU, Kyiv, Ukraine 

One of the perspective materials for the development of 2D photonic structures is 

macroporous silicon that can be obtained by the method of photoanodic etching. In view of 

the potential barrier on a macropore surface or heterojunction on «macropore-nanocoating» 

boundary, one should take into account processes on the local surface centres at energies 

below that of the indirect interband transition. 

Optical absorption in 2D photonic macroporous silicon structures was investigated 

taking into account the linear electro-optical effect. The spectral dependence of optical 

absorption in the near-IR area (impurity absorption) has oscillating structure and varies under 

the “3/2” law at long wavelengths. This correlates with frequency dependence of the 

imaginary part of permittivity for optical transitions between impurity levels and the allowed 

bands of a crystal in an electric field (the impurity Franz-Keldysh effect) [1]. The 

experimental absorption spectra of macroporous silicon agree well with the corresponding 

spectral dependences of the electro-optical energy and the imaginary part of permittivity in 

the weak electric field approximation, thus confirming realization of the impurity Franz- 

Keldysh effect. The electric field of the reflected electromagnetic wave at the grazing angle of 

light incidence onto macropore surface changes effectively a local surface electric field. 

The near-IR light absorption oscillations for 2D macroporous silicon structures with 

microporous silicon and as well as CdTe, ZnO surface nanocrystals were investigated taking 

into account electro-optical effect within the strong electric field approximation. Wellseparated 

oscillations with one order amplitude at spectral ranges of the surface bonds were 

observed. An analysis of the experimental absorption spectra is carried out within the model 

of the resonant electron scattering on impurity states in the strong electric field with 

difference between two resonant energies equaled to Wannier-Stark ladder [2]. The model of 

the resonant electron scattering on impurity states in an electric field of heterojunction 

«silicon-nanocoating» on macropores surface and the realization of Wannier-Stark effect on 

the randomly distributed surface bonds were considered. The Wannier-Stark ladders are not 

destroyed by impurities due to the longer scattering lifetime relatively the oscillation period 

of an electron in an external electric field at all investigated spectral region for macroporous 

silicon structures with CdTe and ZnO surface nanocrystals. 

[1] L.A. Karachevtseva, V.I. Ivanov, O.O. Lytvynenko, K.A. Parshin, O.J. Stronska, Appl. 

Surf. Sci. 255(5), 3328 (2008). 

[2] L. Karachevtseva, S. Kuchmii, O. Lytvynenko, F. Sizov, O. Stronska, A. Stroyuk, Appl. 

Surf. Sci. 257, 3331 (2011). 

60

40th _______________________________________________________________ 


Investigation of multi-phonon excitations in 

ZnO textured crystalline films by Raman spectroscopy 

George V. Lashkarev 1 , Anatoliy M. Yaremko 2 , Vitaliy A. Karpyna 1 

1 I.N.Frantsevich Institute for Problems of Material Science, National Academy of Sciences of 

Ukraine, 3 Krzizhanovsky st., Kyiv, Ukraine 

2 V.E.Lashkarev Institute for Semiconductor Physics, National Academy of Sciences of 

Ukraine, 45 Prospect Nauky, Kyiv, Ukraine 

ZnO is a direct bandgap semiconductor (Eg = 3.37eV at RT) which has got much 

attention due to its ability to generate ultraviolet (UV) radiation. A large binding energy of 

excitons (~60 meV) favors to excitonic transitions at room and higher temperatures. Besides 

ZnO has a strong enough constant of electron- (exciton) phonon interaction (EPI) what 

promtes 8-9 phonon replicas observed in Raman spectrum of this crystal. Investigation of 

photoluminescence (PL) and Raman scattering (RS) spectra are essential for understanding 

the mechanism of light generation and absoorption. In the series of papers the phonon replicas 

in ZnO were revealed in PL and Raman investigations but without theoretical consideration. 

ZnO films were deposited by radio frequency reactive magnetron sputtering on sapphire 

(0001) substrate. To grow textured films of high structural perfectness we used layer-by-layer 

growth mode described in [1]. This growth mode was realized by several stage of deposition 

at which next ZnO layer grow on the previously grown one, in result, ZnO films of improved 

quality is formed. The resonant Raman scattering is a powerful method for the investigation 

of elementary excitations in crystals. Raman measurements were carried out in backscattering 

geometry (z(x,x)z� polarization at which z direction oriented parallel to the c-axis) at room 

temperature using Horiba Jobin Yvon T64000 system, equipped with an Olympus confocal 

optical microscope. The experiment was performed in the wavenumber range from 200 to 

5000 cm -1 with a spectral resolution < 2 cm -1 . 

Multi-phonon structure of RS spectra can be 

Intensity, arb.units 

50 

40 

30 

20 

10 

A LO 

1 

ZnO:Cu/sapphire 

2A LO 

1 

3A LO 

1 4ALO 

5A 

1 

LO 

1 

7A LO 

1 

6A LO 

1 

8A LO 

1 

0 

0 

0 1000 2000 3000 4000 5000 

Raman shift, cm -1 

50000 

40000 

30000 

20000 

10000 

Intensity, arb. units 

Fig.1. Comparison of 

experimental RS spectra 

(curve 1) of ZnO:Cu film with 

calculated one (curve 2). 

1 

2 

explained in the frames of theoretical approach developed 

in [2]. To consider the RS we have to study the response 

of the system on electromagnetic field in the second order 

of perturbation theory. Fig.1 shows experimental RS 

spectrum and theoretical result. It is seen that positions of 

maxima of experimental spectrum are well enough 

described by theoretical dependences. In particular, we 

can see that number of maxima is eight, which is 

practically the same as for good quality bulk crystal [3]. 

The numerical calculations show also that character of 

spectrum, i.e. the number of maxima and distribution of 

intensity different line is very sensitive to constant of EPI. 

The theoretical consideration allows determining 

following main parameters, described LO phonons in RS: 

energy �LO=72 meV, constant of EPI �� 0,1 = 0.2 eV, damping constant � = 10 meV. 

[1] A.I. Ievtushenko, V.A. Karpyna, V.I. Lazorenko, et.al., Thin Solid Films 518 4529 (2010) 

[2] Yaremko A.M., V.M. Dzhagan, V.O. Yukhymchuk, et.al., J. Mol. Struct., 976 205 (2010) 

[3] J. F. Scott, Phys. Rev. B, 2 1209 (1970) 

The authors are grateful to V. Strelchuk for Raman measurements of ZnO films 

61

MoP24 _______________________________________________________________ 


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40th _______________________________________________________________ 


Properties of high-k oxides grown by Atomic Layer Deposition method for 

transparent electronics 

S. Gierałtowska 1 , Ł. Wachnicki 1 , B.S. Witkowski 1 , T.A. Krajewski 1 , M. Godlewski 1,2 , 

E. Guziewicz 1 

1 Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, 

Poland 

2 Cardinal Stefan Wyszynski University, College of Science, Department of Mathematics and 

Natural Sciences, Warszawa, Poland 

Transparent electronics is nowadays an emerging technology for the next generation of 

electronic structures, including IC (integrated circuit), recent devices with 45nm node and 

smaller cross-bar memories and transistors for e-paper applications. The essential materials 

used in semiconductor manufacturing processes are high-k oxides gate dielectrics. The 

introduction of high-k for gate dielectrics is one of several strategies allowing further 

miniaturization of microelectronic components, colloquially referred to as extending the 

Moore's Law. 

Our research was focused on the optimization of technological parameters for composite 

layers of high-k oxides that include hafnium oxide (HfO2) and aluminum oxide (Al2O3). We 

obtain high quality thin films using Atomic Layer Deposition at low temperature (60°C – 

150°C). Growth parameters are elaborated for the maximum smoothness and amorphous 

microstructure required for gating. To fabricate thin film transistors (TFTs) and active 

elements of cross-bar memories, we deposit ZnO (zinc oxide) as an active channel and high-k 

oxides as gate dielectric at low temperature, both grown by the ALD technique. I-V 

characteristics of our TFT structure will be shown. The combination of low temperature and 

transparency processing makes the ZnO-TFT with high-k dielectric very promising for the 

next generation of invisible and flexible electronics. 



65

MoP28 _______________________________________________________________ 


High Spin-Low Spin Transitions in Cu0.2Co0.76Cr1.83Se4 Semiconductor 

E. Maciążek 1 , T. Groń 2 , A.W. Pacyna 3 , T. Mydlarz 4 and J. Krok-Kowalski 2 





4 International Laboratory of High Magnetic Fields and Low Temperatures, 

ul. Gajowicka 95, 53-529 Wrocław, Poland 

Electrical and magnetic studies carried out on single-crystalline CuxCoyCrzSe4 spinels 

showed ferromagnetic ordering and p-type metallic conductivity for y = 0.06, 0.1 and 0.11 as 

well as a ferrimagnetic behaviour and n-type electrical semiconductivity for y = 0.23 [1]. 

Later, structural and electrical investigations carried out on polycrystalline Cu1-xCoxCr2Se4 

spinels in the compositional range 0.0 ≤ x ≤ 1.0 revealed a transformation from cubic to 

monoclinic structure above x = 0.4 as well as metallic-type conductivity with high values of 

activation energy for x ≤ 0.5 and polaron semiconducting with low activation energy for x ³ 

0.8 [2]. Recently, X-ray diffraction studies on the single phase Cu1-xCoxCr2Se4 samples (x = 0, 

0.2, 0.8, 1) proved the existence of the cubic spinel-type structure for x ≤ 0.2 and the 

monoclinic Cr3S4-type one for x ³ 0.8 [3]. Magnetization and magnetic susceptibility of the 

CuxCoyCrzSe4 polycrystals measured in the zero-field-cooled mode showed a transition from 

ferromagnetic order via ferrimagnetic one to antiferromagnetic-like behaviour with increasing 

Co content. This transition was accompanied with a lowering symmetry from cubic to 

monoclinic and for the latter the spin crossover phenomenon occurred [4]. 

Magnetization, dc and ac magnetic susceptibility of Cu0.2Co0.76Cr1.83Se4 were measured 

in the zero-field-cooled mode using a vibrating sample magnetometer with a step motor at 4.2 

K and in applied external magnetic fields up to 150 kOe, a Faraday type Cahn RG automatic 

electrobalance in the temperature range 4.2-370 K and at 800 Oe, and a Lake Shore 7225 ac 

' 

" 

susceptometer, respectively. The in-phase c 1( 

T) 

and out-of-phase c1( T) 

components of the ac 

fundamental susceptibility were recorded in the temperature range 4.2-170 K simultaneously 

as a function of temperature in an oscillating field Hac = 1 Oe with frequency of 120 Hz. The 

signals of the second (c2) and third (c3) harmonics associated with nonlinear susceptibilities 

were detected as a function of temperature using an oscillating field of 5 Oe with frequency of 

120 Hz without the applied external magnetic field. 

' 

Two spectacular peaks were observed on the c1( T) 

curve at 128 K and 147 K which 

corresponded to the strong fall of the dc magnetic susceptibility. At the same temperatures 

these peaks were observed on the curves of the second and third harmonics of magnetic 

susceptibility. Taking into account also a low value of the magnetization of 0.22 µB/f.u. at 4.2 

K and at 140 kOe as well as a hysteresis between 15 kOe and 60 kOe one can conclude that in 

the Cu0.2Co0.76Cr1.83Se4 semiconductor the high spin-low spin transitions may be populated 

and cross over in thermal equilibrium. 

[1] T. Groń, E. Maciążek, J. Heimann, J. Kusz, I. Okońska-Kozłowska, K. Bärner, and Ch. 

Kleeberg, Physica B 254, 84 (1998). 

[2] E. Maciążek, A. Molak, and T. Goryczka, J. Alloys Compd. 441, 222 (2007). 

[3] V. Svitlyk, and Y. Mozharivskyj, Inorg. Chem. 48, 5296 (2009). 

[4] E. Maciążek, T. Groń, A.W. Pacyna, T. Mydlarz, B. Zawisza, and J. Krok-Kowalski, Acta 

Phys. Pol. A 119, (2011). 

66

40th _______________________________________________________________ 


Photoluminescence Study of ZnSe Scintillating Crystals Doped with 

Isovalent Tellurium and Oxygen 

D. Shevchenko 1 , J. Mickevi ius 1 , G. Tamulaitis 1 

N. Starzhinskiy 2 , K. Katrunov 2 , V. Ryzhikov 2 

1 Institute of Applied Research and Semiconductor Physics Department, 

Vilnius University, Sauletekio Ave. 9-III, LT-10222 Vilnius, Lithuania 

2 Institute for Scintillation Materials, 60 Lenin Ave., 61001 Kharkov, Ukraine 

Recently, zinc selenide has attracted considerable attention as a promising scintillating 

material for ionizing radiation detection. Compared to conventional CsI(Tl) scintillators, 

ZnSe –based scintillators have these advantages: considerably lower hygroscopicity, lower 

afterglow level, high light yield, and higher radiation stability (by 3 to 4 orders of magnitude). 

Thus, scintillators based on ZnSe semiconducting compounds are an attractive choice for 

applications in medical and industrial tomography, X-ray introscopy and many others. 

Operating photoemission band in the ZnSe scintillators results from optical transition 

involving deep-defect states. Deep-level-related radiative recombination efficiency can be 

improved by doping with isovalent impurities and subsequent thermal annealing in Zn vapor. 

Introduction of the isovalent impurities promote formation of thermally stable complex 

defects, which act as radiative recombination centers. Subsequent annealing in Zn vapor 

enhances the concentration of the complex defects. Therefore it is important to understand 

radiative and non-radiative recombination mechanisms and their relation with the crystal 

growth conditions. 

The study of deep-level-related photoluminescence was carried out in the ZnSe crystals 

doped with isovalent tellurium and oxygen. Doping of ZnSe by Te was accomplished by 

mixing tellurium into the melt for crystal growth. Two methods of doping with oxygen were 

used: ZnSe(O) sample was doped with O by annealing finelly ground row material in oxygenrich 

atmosphere, while ZnSe(O, Al) sample was doped with oxygen by mixing Al2O3 into the 

melt for crystal growth. Undoped ZnSe samples were also studied for reference. After growth, 

all the samples under study were annealed in Zn vapor in identical conditions. 

Photoluminescence (PL) spectra were measured under steady-state conditions using CW 

He-Cd laser as an excitation source. The wavelength dependence of the absolute quantum 

yield was measured using an integrating Ulbricht sphere. Monochromated light of a halogen 

lamp was used for PL excitation. 

It was determined that photoluminescence quantum yield depends on excitation photon 

energy. The quantum yield rapidly decreases when the excitation photon energy is increased 

above the ZnSe band gap. The highest quantum yield (~ 22 %) is observed in the sample 

doped with tellurium and annealed in Zn vapor. The quantum yield of this sample was by a 

factor of 2 higher than that in other crystals. The observed dependence of the quantum yield 

on excitation wavelength is explained by nonradiative carrier recombination on crystal surface 

and direct excitation of donor-acceptor pair luminescence in ZnSe crystal volume. 

The study of PL spectra showed that the deep–level–related photoemission efficiency 

can be also enhanced by doping with oxygen. PL intensity of ZnSe(O, Al) scintillating crystal 

is by a factor of 16 higher than that of ZnSe(O) scintillator. The photoluminescence spectra 

consist of two strongly overlapped bands due to recombination via M- and SA-type complex 

defects. Annealing results in an increase of PL intensity by factor of ~3 and a red-shift of the 

PL band, compared with those in unannealed crystals. 

67

MoP30 _______________________________________________________________ 


Native Deep-Level Defects in MBE-Grown p-Type CdTe 

Karolina Olender, Tadeusz Wosiński, Andrzej Mąkosa, Piotr Dłużewski, 

Valery Kolkovsky and Grzegorz Karczewski 

Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland 

We present results of investigation of deep-level defects in p-type CdTe layers grown by 

the molecular-beam epitaxy (MBE) technique. The CdTe layers of 5 µm thickness were doped 

with nitrogen and grown on (001)-oriented p+-type, Zn-doped GaAs substrate. Prior to 

deposition of the investigated CdTe:N film, the GaAs substrate was covered with thin, 3monolayer-thick, 

undoped ZnTe layer to reduce the strong lattice mismatch between CdTe and 

GaAs and to stabilize the growth in the [001] direction. 

Deep-level transient spectroscopy (DLTS) was used to identify a set of deep electronic 

states in the band gap of p-CdTe layer employing Schottky barriers, obtained by sputtering 

aluminum. Room-temperature free carrier concentration in the CdTe layers was 

2.4 × 10 16 cm -3 , as found from capacitance–voltage measurements recorded at a frequency of 

1 MHz. 

DLTS measurements, carried out in the temperature range from 90 to 400 K, showed 

five hole traps, at low concentrations of the order of 10 13 cm -3 , called H1 to H5. Explicit 

saturation of the dependence of DLTS-signal amplitude on the filling-pulse time was observed 

for the H2 and H3 traps. They were characterized by the exponential kinetics of carrier 

capture, which means that the observed DLTS peaks originate from isolated point defects or 

impurities. The H2 trap, with the activation energy for hole emission of 0.46 eV, most likely is 

the same trap, which we observed as a minority-carrier trap in n-type CdTe:I layer [1]. We 

attributed this trap to the Cd vacancy, VCd. The H3 trap, with the activation energy of 0.75 eV, 

has been tentatively ascribed to the complex formed of VCd and the Te antisite defect, TeCd. 

In the case of H1 and H4 traps the dependence of DLTS-signal amplitude on the filling- 

pulse time, observed over the range of four orders of magnitude of the time, was logarithmic. 

It suggests that the observed traps are related to the hole states of dislocations. Thorough 

analysis of the dependence of DLTS-peak shape on the filling time allowed us to determine 

the type of electronic states associated with these dislocations. The H1 trap, with the 

activation energy of 0.22 eV, is characteristic of localized states. On the other hand, the H4 

trap, with the activation energy of 0.49 eV, was assigned to the bandlike states of dislocations. 

Probably, an electron emission from the same dislocation states was observed in our DLTS 

experiments for n-type CdTe:I epitaxial layers [1]. We attributed both the H1 and H4 traps to 

threading dislocations, generated at the mismatched interface with the substrate and 

propagated through the CdTe layer. 

Finally, the H5 trap, displaying the logarithmic capture kinetics, has been associated 

with acceptor states at the CdTe surface. We observed a strong influence of electric field on 

the DLTS-peak position of this trap and its apparent activation energy. Measurements of the 

electric-field dependences of hole emission rates, performed at various temperatures, allowed 

us to determine the mechanism responsible for the field-induced enhancement of hole 

ionization rate from the traps as the phonon-assisted tunnelling. 

This work has been partially supported by the Polish Ministry of Science and Higher 

Education under Grant No. N N515 0719 37. 

[1] K. Olender, T. Wosinski, A. Makosa, S. Kret, V. Kolkovsky and G. Karczewski, Semicond. 

Sci. Technol. 26, 045008 (2011). 

68

40th _______________________________________________________________ 


Residual Paramagnetism at High-Temperature Semiconductors 

CuEu2W2O10 and Cu3Eu2W4O18 

P. Urbanowicz 1 , E. Tomaszewicz 2 , T. Groń 1 , H. Duda 1 and Z. Kukuła 1 


2 West Pomeranian University of Technology, Department of Inorganic and Analytical 

Chemistry, Al. Piastów 42, 71-065 Szczecin, Poland 

CuEu2W2O10 and Cu3Eu2W4O18 were synthesized by the solid-state reaction method 

using CuWO4 and Eu2WO6 as the starting materials. The CuEu2W2O10 and Cu3Eu2W4O18 

compounds crystallize in the monoclinic and triclinic system, respectively [1]. Copper 

tungstate, CuWO4, belongs to the triclinic distorted wolframite type structure [2–4] in which 

every metal ion is surrounded by six oxygen ions. It has a potential technological significance 

(scintillation detectors, optical fibres). Thin film of CuWO4 is expected to be a promising 

positive electrode material for high-performance rechargeable lithium batteries [5,6]. On the 

other hand, doped and undoped rare-earth metal molybdates and tungstates (e.g., Eu2WO6) are 

host candidates for luminescent applications. They are used for a fabrication of white lightemitting 

diodes showing high stability, energy-saving and safety [7,8]. In the case of Eu2WO6 

narrower multiplet widths comparable to the thermal energy cause a weak temperature 

dependence of the magnetic susceptibility without the Curie-Weiss region as well as a low ntype 

conduction [9]. 

The magnetic susceptibility of the powder compounds under study was measured in the 

temperature range 2-300 K in the applied external magnetic fields H = 5 kOe using a SQIUD 

Magnetometer of the Quantum Design MPMS – XL – 5 type. The electrical resistivity has been 

measured by a four-probe dc method using the apparatus with Keithley K181 digital 

multimeters. The thermoelectric power was measured by a differential method using the 

temperature difference of about 2 K. For electrical measurements the powder samples were 

compacted to disc form (10mm in diameter and 1–2 mm thick) using a pressure of 1.5GPa 

and they were next sintered through 2 h at 873 K. 

The electrical and magnetic measurements of CuEu2W2O10 and Cu3Eu2W4O18 showed a 

residual paramagnetism, i.e. a low value of the magnetic susceptibility and its weak 

temperature dependence as well as a semiconducting behaviour at high temperatures. We 

have also found that the effective magnetic moment increases gradually from 0.5 µB at 2 K to 

5 µB at 300 K, suggesting a transition from the low spin (LS) state of Eu 3+ ions to their LS and 

high spin (HS) mixed states, as the effective number of Bohr magnetons (peff = 9.80 for S = 3, 

HS) has not been reached. It means that only 50 % conversion of the molecules from LS to 

HS occurred. This work is partly founded from science Grant No. N N209 336937. 

[1] E. Tomaszewicz, J. Typek, and S.M. Kaczmarek, J. Therm. Anal. Calorim. 98, 409(2009). 

[2] L. Kihlborg, and L. Gebert, Acta Crystallogr. B 26, 1020 (1970). 

[3] S. Klein, and H. Weitzel, J. Appl. Crystallogr. 8, 54 (1975) (in German). 

[4] P.F. Schofield, K.S. Knight, S.A.T. Redfern, and G. Cressey, Acta Crystallogr. B 53, 102 

(1997). 

[5] L.G. Van Uitert, and S.T. Preziosi, J. Appl. Phys. 33, 2908 (1962). 

[6] R.H. Gillette, Rev. Sci. Instrum. 21, 294 (1950). 

[7] S. Neeraj, N. Kijima, and A.K. Cheetham, Chem. Phys. Lett. 387, 2 (2004). 

[8] T. Kim, and S. Kang, J. Lumin. 122–123, 964 (2007). 

[9] P. Urbanowicz, E. Tomaszewicz, T. Groń, H. Duda, A.W. Pacyna, and T. Mydlarz, Physica 

B 404, 2213 (2009). 

69

MoP32 _______________________________________________________________ 


Ferromagnetic nanocomposite Co-Al2O3 as a spintronic material with 

engineered magnetic properties 

M.V. Radchenko 1 , G.V. Lashkarev 1 , M.E. Bugaiova 1 , V.I. Sichkovskyi 1 , 

V.I. Lazorenko 1 , L.A. Krushynskaya 2 ,Y.A. Stelmakh 2 , W. Knoff 3 , T. Story 3 

1 I.M. Frantsevych Institute for Problems of Material Science, National Academy of Sciences 

of Ukraine, 3 Krzhizhanovskogo str., Kyiv, Ukraine 

2 E.O.Paton Electric Welding Institute, Academy of Sciences of Ukraine, 68 Antonowich str., 

Kyiv, Ukraine 

3 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, Warsaw, Poland 

Ferromagnetic cobalt nanoparticles (NP) embedded in alumina matrix constitute a new class 

of two-phase spintronic materials - ferromagnetic nanocomposites (FMNC). FMNC attract 

attention as artificially developed materials permitting efficient engineering of their magnetic 

and magnetotransport properties These materials are closely related to inhomogeneous diluted 

magnetic semiconductors containing ferromagnetic clusters. In this work, we study magnetic 

and electrical characteristics of Cox(Al2O3)100-x (x

40th _______________________________________________________________ 


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71

MoP34 _______________________________________________________________ 


Van der Waals surface of InSe as a standard nanorelief in the metrology of 

nanoobjects 

Dmitriev A. I. 

. I. M. Frantsevich Institute for Problems of Material Science, National Academy of 

Sciences of Ukraine, Krzhizhanivskogo st. 3, 03680 Kyiv, Ukraine, FAX: +38424-2131. 

E-mail: dmitr. kiev@gmail.com 

Development of new high technologies and new materials leading to the fundamental 

improvment of the technical level of production largely dependents on the level of metrological 

support. Intensive development of nanotechnology requires high-precision measurements on 

atomic and molecular levels by creating the metrological system for measurements, at the first 

turn, the length in the nanometer scale. Such measurements require standard samples of 

nanorelief surface. 

At present, the nanorelief surface of highly oriented pyrolytic graphite (HOPG) is used for 

this purpase. Simultaneously with the scanning of an unknown surface the scan of the well- 

known surface of graphite (the period of the hexagonal crystal lattice: a = 2,464 ± 0,002 Ǻ) is 

carried out. Software recognition of atoms image of the graphite allows to generate a control 

signal for correcting the microscope manipulator. When cleaving HOPG many stages with 

dimensions less than 2x2 mm are formed. They are used as a model of nanorelief They appear 

at fracture of graphite planes, oriented not toward cleavage. Graphite planes have structural 

defects associated with dislocations. Different types of dislocations manifest themselves in the 

topography of the surface in many ways. Over time, the accumulation of the adsorbate on the 

surface, results in poor quality images. 

Semiconductor InSe belongs to a group of layered compounds A3B6.Each layer of this 

crystal consists of atomic groups Se-In-In-Se with strong covalent bonds in the layer. Se atoms 

of neighboring layers are linked by weak Van der Waals (VdW) forces and form VdW surface. 

High chemical stability and the absence of dangling bonds (defects) prevents the appearance of 

the adsorbat. Low surface roughness of cleaved surface at the areas up to 5x5 mm allows to 

use the VdW surface of InSe single crystals as the standard nanorelief. This is evidenced by 

the researches of morphology for VdW surface by scanning tunneling microscopy [1] in which 

images with atomic resolution were obtained. A single crystal InSe, grown by vertical 

Bridgman-Stockbarger method. The crystal has -g-polytype rhombohedral structure . with 

periods a = 4.003 Å, and c = 24.9553 Å (in hexagonal axes). 

Thus InSe is appropriate standard nanorelief for probe microscopy. 

1. Physics of the Solid State,53, 3, 622 (2011). 

72

40th _______________________________________________________________ 


Crystal field analysis of the Yb 3+ energy level scheme in III-V 


A. Kami�ska 1 , C.-G. Ma 2 , M.G. Brik 2 , A. Kozanecki 1 , M. Bo�kowski 3 , E. Alves 4 , 

A. Suchocki 1,5 

1 Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland 

2 Institute of Physics, University of Tartu, Riia 142, Tartu 51014, Estonia 

3 Institute of High Pressures Physics ‘Unipress’, Polish Academy of Sciences, 01-142 Warsaw, 

Poland 

4 Instituto Tecnologico e Nuclear, Estrada Nacional 10, 2686-953 Sacavém, Portugal 

5 Institute of Physics, University of Bydgoszcz, Weyssenhoffa 11, 85-072 Bydgoszcz, Poland 

Rare earths (RE) doped semiconductors are nowadays attracting a lot of attention due 

to their unique optical and electrical properties and high potential of these materials in new 

optoelectronic device applications, for instance in electrically-pumped light-emitting diodes 

or lasers [1]. Among the RE doped III–V semiconductors InP:Yb is one of the most 

intensively studied material. Recently an important effort has been devoted also to study the 

optical properties of ytterbium doped GaN [2, 3]. These materials reveal strong Yb-related 

luminescence at about 1 �m. Yb 3+ ions (4f 13 electron configuration) have a simple energy 

level scheme, which consists of two states only: 2 F7/2 and 2 F5/2 separated by about 

10 000 cm -1 . Such a scheme excludes excited state absorption and all related energy losses. 

From this point of view, Yb 3+ ion is now the most promising for use as a non-Nd lasing center 

in the infrared spectral region. 

In the present work we report on combination of the high-pressure measurements with 

use of diamond anvil cell (DAC) of the luminescence spectra of InP:Yb 3+ and GaN:Yb 3+ 

crystals with ab initio calculations of the electronic and optical properties of these systems. 

The CASTEP module [4] of the Materials Studio was used to calculate the electronic and 

optical properties at ambient and elevated pressure. In addition, crystal field analysis of 

splitting of the 2 F7/2 and 2 F5/2 states has been performed, with an aim of assigning all features 

of the experimental luminescence spectra. 

A thorough analysis of the pressure behavior of the Yb 3+ luminescence lines in InP 

reveals interesting effects, namely: after 6 GPa blue shift of the luminescence tends to 

saturation, which was explained by pressure-induced shift of the InP valence band 

approaching the energies of the Yb 4f-4f transitions. This overlap behaves exactly as the 

luminescence lines with pressure. An analysis of the pressure dependence of the Yb 3+ 

luminescence in GaN and fitting the trigonal crystal field Hamiltonian to the experimental 

data allowed to determine the ambient pressure values of crystal field parameters, spin orbit 

parameter and their pressure coefficients. 

Acknowledgements: This work was partly supported by the European Union within 

European Regional Development Fund, through the Innovative Economy grant 

(POIG.01.01.02-00-108/2009/2) and the project No. N N202 203838 of Polish Ministry of 

Science and Higher Education. 

References: 

[1] J. H. Park et al., J. Appl. Phys. 98, 056108 (2005). 

[2] W.M. Jadwisienczak et al., Opt. Mater. 23, 175 (2003), 

[3] T. Koubaa et al., J. Alloys Compd. 496, 56 (2010). 

[4] M. D. Segall et al., J. Phys.: Condens. Matter 14, 2717 (2002). 

73

MoP36 

_______________________________________________________________ 


Studies of Electric Transport Properties of Single Layer Devices 

Based on the Polyazomethine Thin Films 

J. Weszka, M. Domański, J. Jurusik, B. Hajduk, M. Chwastek, 

and H. Bednarski 

Centre of Polymer and Carbon Materials, Polish Academy of Sciences, 34 M. 

Curie-Sk̷lodowska Str., 41-819 Zabrze, Poland 

Organic semiconductors (OS) have been known since a many years for their great potential 

applications in opto-electronic devices. Among the conjugated polymers, poly(pphenylenevinylene) 

(PPV) and its derivatives (like MEH-PPV) belong to the family 

of more extensively studied OSs and are known as revealing good properties for optoelectronic 

applications. Poly (p-phenyleneazomethine) (PPI), much less known and studied 

polymer than PPV, being its iso-elctronic counterpart and having nearly the same 

electronic structure, though containing nitrogen atoms in the backbone, has appeared to 

be very promising for optoelectronic applications, too [1,2]. 

Single-layer organic devices have been produced based on chemical vapour deposited, 

in a homemade technological set-up [3]. Polyazomethine thin films were grown via polycondensation 

process of aromatic diamine and dialdehyde and sandwiched between metal 

electrodes with different work functions. The choice of the electrodes has appeared to 

influence greatly the device properties. For these reasons various pairs of electrode materials 

were used from ITO, Al and Au in order to check practically conditions of Schottky 

barrier formation and their applicability for photovoltaic devices. Metallic electrodes were 

thermally evaporated under vacuum of 10 −6 Tr, otherwise glass substrates covered with 

ITO layer were used. 

To verify quality of the as-prepared devices current-voltage characteristics have been 

taken as well as measurements of the current dependence on time were performed. Results 

have been analysed in terms of the unified device model for single layer organic light 

emitting diodes or photovoltaic cells with charge injection, transport and space charge 

effects [4]. The model describes both injection limited and space charge limited current 

flow and the transition between them. Determined by us relatively high value of the 

Schottky barrier height (higher then 0.5 eV) suggests that the current flow in the asprepared 

devices is injection charge limited, which is further supported by the net injected 

charge being relatively small. Therefore, for small bias voltage in the injection limited 

regime the thermionic emission is the dominant injection mechanism. 

Relatively low currents density, in comparison to those reported for PPV, recorded 

for our studied PPI based devices is attributed to the presence of surface states on the 

side of high work function electrode rather than to steric differences in the backbones of 

the two polymers. This is consistent with the results we obtained on MEH-PPV devices 

prepared for comparison reasons. 

[1] A. Iwan and D. Sek, Prog. Polym. Sci. 33 (2008) 289-345. 

[2] J. Weszka, H. Bednarski and M.Domanski, J. Chem. Phys. 131 (2009) 024901. 

[3] J. Weszka, M. Domanski, B. Jarzabek, J. Jurusik, J. Cisowski, A. Burian, Thin 

Solid Films 516 (2008) 3098. 

[4] P.S. Davids, I.H. Campbell, and D.L. Smith, J. Appl. Phys. 82 (1997) 6319. 

74

40th _______________________________________________________________ 


Optical properties of black silicon with precipitated silver and gold 

nanoparticles 

R. Jarimavi i t -Žvalionien 1 , I. Prosy evas 1 , Ž. Kaminskien 1 , S. Lapinskas 2 

1 Institute of Materials Science, Kaunas University of Technology, Savanoriu pr. 271, Kaunas, Lithuania 

2 Institute of Applied Research, Vilnius University, Sauletekio str. 10, Kaunas, Lithuania 

Black silicon (BS) is a new generation material which may be useful for many 

applications, such as lasers, gas sensors, solar cells and etc. Black silicon (BS) is a type of porous 

silicon with low light reflectance and high light absorbance values. BS layers are especially 

useful and important in solar energy conversion. Forming BS layers on silicon increase the 

effective area and light absorbance as well as solar conversion efficiency. Another new way to 

increase solar energy conversion is use surface plasmons, i.e., collective surface oscillations of 

conducting electrons in metal nanostructures that tend to trap optical waves near their surface. 

Plasmonics is a rapidly emerging subfield of nanotechnologies, which gives a possibility to 

control and guide light interaction with matter more effectively. Noble metals like silver and 

gold are ideal for this purpose as they do not have many interband transitions and do not absorb 

much light as a result. By combining black silicon with precipitated plasmonic nanoparticles in 

active layer has the potential to increase light interaction with matter more effectively and can 

revolutionary change the market of solar cells. 

Etching of silicon and formation of porous surfaces can be performed by many different 

methods. But the most simple in use is chemical metal assisted etching. In this work the porous 

silicon plates were prepared by wet chemical metal assisted method in a 1-minute single step 

liquid etch based upon catalysis by silver nanoparticles formed in a solution containing HF, V2O2 

and AgNO3. Processing time was reduced to 10 seconds by heating the samples at 80 o C. For 

synthesis of plasmonic nanoparticles silver nitrate (AgNO3) and chloroauric acid (HAuCl4) were 

used. 

Scanning electron microscope (SEM) analysis was done in order to evaluate the form and 

size of formed pores before precipitation of plasmonic nanoparticles and morphology of surface 

of porous silicon after precipitation. Optical properties of black silicon samples were investigated 

with UV-VIS and FTIR spectrometers and reflectance spectra were recorded during porous 

silicon formation at different times. 

SEM analysis of PS exhibited oval-shaped pores with Ø 150 – 200 nm and Ø 50 – 100 

nm in samples with longer and shorter processing times respectively. SEM analysis of BS with 

precipitated nanoparticles has revealed non-uniform distribution of gold and silver nanoparticles 

(Ø 70 - 150 nm) on BS surface and inside of pores. Reflectance analysis of BS has revealed that 

reflectance decreases with increase of processing time, herewith with pores depth, and increases 

after precipitation of nanoparticles in both cases. This phenomenon is still under investigation, 

but in general we can conclude, that formation of BS was successful and precipitation of 

nanoparticles on its surface gives a possibility to control reflectivity of BS surfaces and increase 

photo efficiency through enhanced plasmonic properties of gold and silver nanoparticles. 

75

MoP38 _______________________________________________________________ 


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76

40th _______________________________________________________________ 


Self-Compensation Mechanism in Semi-Insulating CdMnTe:Sn Crystals 

Intended for X/γ-Ray Detectors 

N.S. Yurtsenyuk, L.A. Kosyachenko, V.M. Sklyarchuk, 

O.L. Maslyanchuk, E.V. Grushko 

Chernivtsi National University, Optoelectronics Department, 58012 Chernivtsi, Ukraine 

Cd1-xMnxTe is a typical diluted magnetic semiconductor with the zinc-blende structure 

within the 0 < x < 0.77 range. Owing to its unique magnetic and magneto-optic properties, 

Cd1-xMnxTe crystals can be used in many device applications, such as Faraday rotators, 

optical isolators, solar cells, magnetic field sensors and substrates for the epitaxial growth of 

Hg1-xCdxTe and Hg1-xZnxTe [1]. More recently, Cd1-xMnxTe offers several potential 

advantages over Cd1-xZnxTe as a material for room-temperature X/γ-ray detectors [2,3] that 

are widely used in science, medicine, industry, environment monitoring and other fields. 

Cd1-xMnxTe has a wide range of tunability of the band gap due to the large compositional 

influence of manganese. The band gap range 1.7 eV to 2.2 eV, required for substantiating an 

“ideal” radiation detector performance, can be realized with a relatively low (< 50%) amount 

of Mn compared with that of Zn in Cd1-xZnxTe (up to 70%) [4]. In fact, the energy band gap 

of Cd1-xMnxTe increases about 13 meV per atomic percent of Mn compared with 6.7 meV of 

Zn in Cd1-xZnxTe. Another important advantage is that the segregation coefficient of Mn in 

CdTe is approximately 1 compared with 1.35 for Zn, that is, Cd1-xMnxTe crystals can have a 

more homogenous distribution of Mn throughout the ingot. These notable characteristics of 

Cd1-xMnxTe increase the possibility of growing uniform large-volume stoichiometric crystals 

that can potentially be fabricated into different high-quality devices. 

In this work we study the conductivity mechanism of Cd1-xMnxTe single crystals doped 

by Sn. It is known that the introduction of Sn in the CdTe, as well as in other II-VI 

semiconductors, accompanied by the formation of complexes and self-compensation of 

conductivity and leads to a semi-insulating state of the semiconductor, which is very 

important from the standpoint of its use in X/γ-ray detectors. We set a goal to find the 

ionization energy of the level responsible on electrical conductivity Ei of the material and the 

degree of its compensation ξ = Na/Nd. The band gap and its temperature dependence 

(necessary for calculations) were found from the optical transmission curves in the range of 

the absorption edge of semiconductor. Based on the experimental dependences of the 

electrical characteristics of the material and statistics of electrons and holes, we have 

succeeded in determining Ei and ξ. Such a degree of compensation reveals to be close to 

100%. This is a direct confirmation of self-compensation, which provides semi-insulating 

state of the semiconductor. It seems that the obtained results lead to the conclusions which are 

important for technology. 

[1] J.K. Furdyna, J. Appl. Phys. 64(4), R29 (1988). 

[2] A. Burger, K. Chattopadhyay, H. Chen, J.-O. Ndap, X. Ma, S. Trivedi, S.-W. Kutcher, R. Chen, 

and R.-D. Rosemeier. J. Cryst. Growth 198/199, 872 (1999). 

[3] A. Mycielski, A. Burger,M. Sowinska, M. Groza, A. Szadkowski, P. Wojnar, B.Witkowska, 

W.Kaliszek, and P. Siffert, Phys. Stat. Sol. (c) 2, 1578 (2005). 

[4] J.E. Toney, T.E. Schlesinger, and R.B. James, Nucl. Instr. & Meth., A428, 14 (1999). 

77

MoP40 _______________________________________________________________ 


Influence of Cu, Ga and Au Dopants and Technology Conditions on the 

Magnetic Interactions in HgCr2Se4 Single Crystals 

J. Krok-Kowalski 1 , G. Władarz 1 , T. Groń 1 , H. Duda 1 , A.W. Pacyna 2 , K. Nikiforov 3 and 

P. Rduch 1 

1 University of Silesia, Institute of Physics, ul. Uniwersytecka 4, 40-007, Katowice, Poland 



3 Physico-Mathematical Faculty, K. Tsiolkovski State Pedagogical University, 

St. Razin str. 26, Kaluga 248023, Russia 

It is well known, that in the ferromagnetic spinel compound HgCr2Se4 (where TC and 

CW are of order 100 K and 150 K respectively) the divalent Hg 2+ ions occupy tetrahedral 

positions only, whereas trivalent Cr 3+ ions are located only in octahedral positions. 

Ferromagnetic coupling of the magnetic moments in this compound is realized via 

superexchange magnetic interactions [1]. It is also well known, that the full substitution in the 

tetrahedral positions of the divalent Hg 2+ ions by the monovalent, e.g. Cu + ions, leads to both 

the mixed valence of the chromium ions (it means, Cr 3+ and Cr 4+ in the ratio 1:1) and to the 

appearance and domination of the another mechanism of the magnetic coupling giving very 

strong ferromagnetic coupling, namely double exchange interaction. In this case both TC and 

CW become of order of 400 K [2,3]. However, the substitution of the Hg 2+ ions by the 

trivalent ions, e.g. Ga 3+ , leads to the collinear antiferromagnetism being the result of the 

superexchange interaction only, with the concentration of Ga 3+ ions up to 50%. The one aim 

of this work is to investigate how influences the substitution of Hg 2+ ions by Cu + , Au 2+ and 

Ga 3+ ions on the magnetic ordering in the sample, when the concentration of the substituting 

ions is lower than 10 %. The another one concerns of the influence of technology conditions 

on magnetic ordering in the sample. 

Using the chemical transport method the single crystals of HgCr2Se4 doped with copper 

(7%), gallium (8%) and gold (2%) were obtained. Additionally, the two non doped single 

crystals of HgCr2Se4 were obtained, in different synthesis conditions. One of them was 

synthesized with the deficiency of Hg (this procedure the produces vacancies), another one 

with Hg excess (this procedure brings to elimination of vacancies). For all crystals under 

study both the dc and ac magnetic susceptibility was measured in the temperature range of 

4.2 – 250 K. The dc measurements were carried out with the use of the Cahn magnetic 

balance and SQUID susceptometer, whereas the ac measurements were carried out with the 

use of the Lake Shore 7225 magnetometer. 

As it follows from the obtained results, substitution monovalent Cu + ions and divalent 

Au 2+ ions in place of Hg 2+ ions causes the increase of the Curie temperature in comparison 

with the Curie temperature of undoped HgCr2Se4. Substitution of Hg 2+ ions by trivalent Ga 3+ 

ions causes the lowering of TC. On the other hand, ZFC and FC measurements of the 

magnetic susceptibility shows that in the samples containing Cu + and Ga 3+ some trace 

frustration of magnetic interactions in spite of their ferromagnetic ordering occurs. Similar 

effect have been observed for single crystal synthesized with the deficiency of Hg. The latter 

effect is caused by the occurrence of vacancies generated in the sample by the technological 

process. 

[1] P.K. Baltzer, P.J. Wojtowicz, M. Robbins, and E. Lopatin, Phys. Rev. 151, 367 (1966). 

[2] F.K. Lotgering, Proc. Int. Conf. on Magnetism, Nottingham England, (1964) 533. 

[3] J. Krok, J. Spałek, J. Juszczyk, and J. Warczewski, Phys. Rev. B 28, 6499 (1983). 

78

40th _______________________________________________________________ 


The Photodetectors with Vertical Integration Based on ZnO Films 

A.I. Ievtushenko 1 , G.V. Lashkarev 1 , V.I. Lazorenko 1 , Zs.J. Horvath 2,3 , M.G. Dusheyko 4 

1 Frantsevich Institute for Problems of Materials Science, NASU, Kyiv, Ukraine 

2 Research Institute for Technical Physics and Materials Science, HAS, Budapest, Hungary 

3 Institute of Microelectronics and Technology, Budapest, Hungary 

4 National Technical University of Ukraine “KPI”, Kyiv, Ukraine 

ZnO is a wide-band (Eg 3.3 eV) direct-gap material which attracts a great attention to 

the development of the photodetectors for near-ultraviolet range. It is an electronic analog of 

GaN, but ZnO have economic and ecological benefits in comparison with GaN. There are 

many papers devoted to the formation detectors of a planar configuration [1]. One of the 

promising directions of microelectronics is the development and study of devices with a 

vertical structure. The reason is that in this vertical configuration of electrodes the 

interelectrode distance can be easily reduced without using expensive lithography processes. 

Therefore, the purpose of this report is devoted to the study of technological aspects for the 

deposition of ZnO films as well as the investigation of the photoelectrical properties of 

structures with vertical configuration of the electrodes. 

Early we reported the positive role of nitrogen in ZnO for UV detectors [2]. Therefore, 

the undoped and nitrogen doped ZnO films with different concentrations of the nitrogen were 

deposited by magnetron sputtering on n-Si and ITO/glass substrates. Structural and optical 

properties of the films were examined by XRD, EDX and optical measurements. Aluminum 

as ohmic contact to Si and Ni as Schottky contact to ZnO were deposited by electron beam 

evaporation with thickness control. Ni/ZnO/n-Si/Al and Ni/ZnO/ITO layered structures of 

photodetectors were obtained. Current-voltage curves of photodiodes were studied in dark and 

under visible and UV irradiations using Keithley-236 Source Measure Unit. Features of the 

current-voltage characteristics and leakage current mechanisms are discussed. It was found an 

increase of photosensitivity with increasing nitrogen concentration in nitrogen doped ZnO 

films for all types of vertical structures. The maximum enhancement of reverse current under 

UV irradiation was two orders of magnitude. The influence of deposition technology of ZnO 

films on the photoelectrical properties of detectors as well as the effect of nitrogen 

incorporation will be presented. Prospects for the application of ZnO photodetectors with 

vertical integration and requirements for their design will be discussed. 

[1] K. Liu, M. Sakurai, M. Aono Sensors, 10, pp.8604-8634 (2010). 

[2] A.I. Ievtushenko, G.V. Lashkarev, V.I. Lazorenko, et al. Phys. Stat. Sol. ( ), 207, 7, pp. 

1746–1750 (2010). 

79

MoP42 _______________________________________________________________ 


Features of the Properties for Nitrogen Doping and Al-N Codoping of ZnO 

Films 

A.I. Ievtushenko 1 , G.V. Lashkarev 1 , V.I. Lazorenko 1 , O.Y. Khyzhun 1 , L.O. Klochkov 1 , 

O.I. Bykov 1 , V.M. Tkach 2 , V.A. Baturin 3 , A.Y. Karpenko 3 


2 Bakul Institute for Superhard Materials, Kyiv, Ukraine 

3 Institute of Applied Physics, Sumy, Ukraine 

Now zinc oxide is almost the most investigated material in the world because of its 

physical, ecological and economic benefits which make it promising one for photonic, 

optoelectronic and acoustooptic devices, etc. However the properties of ZnO films strongly 

depend on the concentration of various defects appearing at the stages of film growth and 

further processes in as-grown ZnO films. 

The nitrogen in ZnO is an acceptor impurity and widely used in attempts to obtain 

stable p-type conductivity in ZnO. However, based on our previous studies, we think that 

nitrogen doping leads to the passivation of oxygen vacancies of ZnO and therefore increase 

the photosensitivity, response speed and stability of photodetectors on their basis. Little 

known fact is the effect of increasing the concentration of nitrogen in ZnO films on their 

physical properties by using the increase of nitrogen pressure in the chamber at magnetron 

deposition. It is promising to investigate the way of increasing of nitrogen solubility in ZnO 

by using Al-N codoping. 

ZnO:N films with different nitrogen concentration were deposited on Si, SiNx and 

quartz substrates by magnetron sputtering using Zn, Zn:0.7%Al and Zn:1.4%Al targets. The 

investigations of XRD, AFM, PL, X-ray photoelectronic and EDX spectroscopy were carried 

out. In this report the influence of different types of nitrogen doping on the transformation of 

the structure, optical properties and morphology of ZnO:N films will be presented. 

80

40th _______________________________________________________________ 


Influence of Oxygen Pressure on the Properties of AZO Films 

A.I. Ievtushenko 1 , G.V. Lashkarev 1 , V.I. Lazorenko 1 , L.O. Klochkov 1 , O.I. Bykov 1 , 

O.M. Kutsay 2 , S.P. Starik 2 , V.A. Baturin 3 , A.Y. Karpenko 3 


2 Bakul Institute for Superhard Materials, Kyiv, Ukraine 

3 Institute of Applied Physics, Sumy, Ukraine 

New oxide materials are very attractive for replacement of existing traditional ones in 

various fields of electronics and optoelectronics. Particularly the problems of creation the 

transparent conductive electrodes based on them attract more attention. 

The major drawback of widely-used ITO is a limited world reserve of indium. 

Opposite to ITO, zinc oxide has ecological and economical benefits and its components are 

widely distributed in Earth. Therefore, doped with aluminum (AZO), gallium (GZO) or 

indium (IZO) ZnO films are the best suited candidates to replace ITO. The development of 

technology for deposition of transparent conductive electrodes based on AZO films will have 

the commercial future. 

Therefore the high quality aluminum doped ZnO films were deposited on glass 

substrates by layer by layer deposition method at a magnetron sputtering of Zn:1.4%Al target. 

The report presents the results of oxygen pressure influence on structural, morphological, 

electrical and optical properties of AZO films. It is demonstrated that optimal oxygen pressure 

of 0.03 Pa in the deposition chamber leads to the following AZO films characteristics: the 

resistivity is about 10 -3 Ohm cm, transparency - 95% and roughness - 6 nm. Our results on 

investigation of AZO films magnetron deposition technology will be discussed as well as the 

prospects of their applications. 

81

MoP44 _______________________________________________________________ 


Thermoelectric Power of CuCrxVySe4 p-Type Spinel Semiconductors 

H. Duda 1 , E. Malicka 2 , T. Groń 1 , A. Gągor 3 , R. Sitko 2 , J. Krok-Kowalski 1 and P. Rduch 1 



3 Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 

ul. Okólna 2, 50-950 Wrocław, Poland 

Detailed studies of the thermoelectric power, electrical conductivity, structural and 

magnetic properties carried out on polycrystalline CuCrxVySe4 spinels with x = 1.79, 1.64 and 

1.49 and y = 0.08, 0.22 and 0.45, respectively, are presented. Powder samples of the 

CuCrxVySe4 spinel series were prepared by annealing stoichiometric mixtures of high purity 

( 99.99 %) elements: Cu, Cr, V and Se. A precise atomic content determination of each 

sample with the aid of the energy-dispersive X-ray spectrometry (EDXRF) showed that the 

polycrystals of the CuCrxVySe4 spinel system revealed the cation deficiencies in the 

octahedral sites because x + y 

y 

2. A Rietveld refinement of the spinels under study was done 

using an X'Pert PRO X-ray diffractometer and a Jana-2000 program package. The electrical 

conductivity has been measured with the four-probe dc method using the apparatus with 

Keithley K181 digital multimeters. The thermoelectric power was measured with a 

differential method using the temperature gradient T of about 2 K. The electrical and thermal 

contacts between the sample and the copper rods were maintained with a silver lacquer 

mixture (Degussa Leitsilber 200). Magnetization and magnetic susceptibility were performed 

using a Faraday type Cahn RG automatic electrobalance at magnetic field up to 7 kOe. The 

electrical and magnetic measurements were done in the temperature ranges 77-432 K and 77- 

550 K, respectively. 

All the compounds under study crystallize in regular system of a normal spinel type 

MgAl2O4 structure with the space group symmetry Fd3m. With increasing V content a lattice 

parameter slightly increases from 1033.66(4) pm for y = 0.08 to 1033.71 (5) for y = 0.45 

while the positional anion parameter decreases from 0.2574(3) for y = 0.08 to 0.2568(3) for y 

= 0.45. The CuCrxVySe4 spinels are ferromagnets for that a Curie temperature TC and a 

paramagnetic Curie-Weiss temperature decrease as the V content increases, i.e. from TC = 

406 K and = 383 K for y = 0.08, via TC = 351 K and = 380 K for y = 0.22 via to TC = 282 

K and = 277 K for y = 0.45. The electrical conductivity measurements revealed the change 

of the hole conductivity character from the semiconductive into the metallic one close to TC. 

The thermoelectric power analysis was done with the aid of the modified Matoba, Anzai and 

Fujimori semi-empirical formula [1] including magnetic contribution [2]. The results of 

thermopower analysis of the spinels under study show that the intensity of the magnon drag 

component is smaller in comparison with the single crystal sample of comparable V-content 

[2]. The magnon excitations, usually driven by the double exchange mechanism, are observed 

only at low temperatures. At higher temperatures the contribution to total thermopower 

originates mainly from the phonon component. At high temperatures, the diffusion component 

dominates and, according to the Mott formula, it is proportional to temperature. The non-zero 

value of the so-called impurity component of the thermopower described by the T 1/2 law 

suggests the presence of cation deficiencies in the octahedral sites. 


[1] M. Matoba, S. Anzai, and A. Fujimori, J. Phys. Soc. Jpn. 63, 1429 (1994). 

[2] E. Malicka, T. Groń, D. Skrzypek, A.W. Pacyna, D. Badurski, A. Waśkowska, S. Mazur, 

and R. Sitko, Philos. Mag. 90, 1525 (2010). 

82

40th _______________________________________________________________ 


Critical Behaviour of the 3D-Heisenberg Ferromagnetic 

Semiconductors CdxCeyCr2Se4 

H. Duda 1 , P. Rduch 1 , E. Malicka 2 , T. Groń 1 and A. Gągor 3 



3 Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 

ul. Okólna 2, 50-950 Wrocław, Poland 

The pure CdCr2Se4 end member of the CdxCeyCr2Se4 spinel system combines the p-type 

semiconducting and ferromagnetic properties with a Curie temperature TC = 142 K and a 

Curie-Weiss temperature qCW = 190 K [1]. Magnetization of CdCr2Se4 reaches the full 

saturation of 5.98 µB per molecule [2] and the ferromagnetic properties are the result of 

dominance of large and positive the nearest-neighbour Cr-Cr interactions [3]. Various 

theoretical models of the critical phenomena, the mean-field, the three-dimensional (3D) 

Heisenberg, the 3D-Ising and the tricritical mean-field model used to explain the critical 

properties showed that the CdCr2Se4 was in best accordance with the 3D-Heisenberg model 

for which the critical exponents: β = 0.36, γ = 1.38 and δ = 4.8 [4,5]. 

The CdxCeyCr2Se4 spinel single crystals under study have a normal cation distribution, 

the Cd and Ce ions being located at the tetrahedral sites, while the Cr ions at the octahedral 

ones. Electrical and magnetic measurements revealed the semiconducting properties and a 

ferromagnetic order with TC = 132 K which insensibly decreases as the Ce content increases 

as well as a strong reduction of magnetic moment from 5.8 µB for y = 0.03 to 1.93 µB for y = 

0.13. The critical exponents of CdxCeyCr2Se4 single crystals were studied by measuring 

isothermal dc-magnetization around the paramagnetic-ferromagnetic (PM-FM) phase 

transition. Isothermal magnetization was measure with the aid of a Quantum Design System 

(MPMS XL) in the magnetic field up to 20 kOe and in the temperature range 125-140 K. 

The critical exponents (TC, β, γ and δ) were determined by analyzing the magnetization 

data in terms of various research techniques including modified Arrott plot [6], Kouvel-Fisher 

method [7], and critical isotherm analysis. Here β and γ are the critical exponents for the 

temperature dependence of the spontaneous magnetization just below TC and inverse initial 

susceptibility just above TC, respectively. In addition, the critical exponent δ is determined 

separately from the isothermal magnetization at TC. The critical exponent values are found to 

be consistent with the Widom scaling relation δ = 1 + γ/β, implying the critical exponents are 

reliable. The critical exponents characterizing the PM-FM transition are: β = 0.367 ±0.013, γ 

= 1.389 ±0.025 and δ = 4.763 ±0.043 at TC = 131 K for the sample Cd0.96Ce0.03Cr2Se4 and β = 

0.350 ±0.003, γ = 1.202 ±0.026 and δ = 4.487 ±0.095 at TC = 134 K for the sample 

Cd0.84Ce0.13Cr2Se4. These values of critical exponents concerning CdxCeyCr2Se4 system are 

close to the theoretical ones predicted by the 3D-Heisenberg model for CdCr2Se4. 


[1] P.K. Baltzer, H.W. Lehmann, and M. Robbins, Phys. Rev. Lett. 15, 493 (1965). 

[2] R.C. LeCraw, H. von Philipsborn, and M.D. Sturge, J. Appl. Phys. 38, 965 (1967). 

[3] P.K. Baltzer, M. Robbins, and P.J. Wojtowicz, J. Appl. Phys. 38, 953 (1967). 

[4] L. Zhang, J. Fan, L. Li, R. Li, L. Ling, Z. Qu, W. Tong, S. Tan, and Y. Zhang, A Letters 

Journal Exploring the Frontiers of Physics (EPL) 91, 57001 (2010). 

[5] W. Zarek, Acta. Phys. Pol. A 52, 657 (1977). 

[6] A. Arrott, and J.E. Noakes, Phys. Rev. Lett. 19, 786 (1967). 

[7] J.S. Kouvel and M.E. Fisher, Phys. Rev. Lett. 136, A1626 (1964). 

83

MoP46 _______________________________________________________________ 


Optical properties of ZnO/ZnMgO single quantum wells grown by 


J.M. Sajkowski, M.A. Pietrzyk, D. Dobosz, M. Stachowicz, A. Droba, E.Przezdziecka, 

A.Wierzbicka, A. Kozanecki, 

Institute of Physics Polish Academy of Sciences, Al. Lotników 32/46 02-668, Warsaw, Poland 

In this work the high quality ZnMgO layers and ZnO/ZnMgO quantum wells (QWs) showing 

no phase separation were grown on (0001) sapphire substrates. ZnMgO layers and 

ZnO/ZnMgO heterostructures were grown at temperatures 445 - 460°C. No specific buffer 

layers were deposited on sapphire. Prior to growth the substrates were annealed in the growth 

chamber in oxygen (p=1,4*10 -5 Torr) at 600° C, and then a ~100 nm ZnMgO (Mg contents 10 

- 20%) barrier layer was grown. Then the growth was interrupted for couple of minutes and 

after this a ZnO wells with different thicknesses were grown. Finally, ZnMgO capping layers 

of the same composition as the ZnMgO barrier were deposited. After growth the structures 

were characterized using X-ray diffraction for the analysis of their crystalline quality and 

AFM was used for surface morphology studies. AFM images revealed very good flatness of 

the surface – rms value was 1-2 nm. 

We present results of optical spectroscopy for a series of ZnO/ZnMgO single quantum wells 

of different widths using photoluminescence. Temperature dependent PL spectra were 

measured within a temperature range of 4-300K. We observed a blue shift of excitonic 

emission in comparison with bulk ZnO values which demonstrates quantum confinement in 

the ZnO wells with thicknesses smaller than 4 nm. We also demonstrate that excitonic 

emission from QWs is dominated by excitons bound to donors. The characteristic energy of 

PL decay of the dominant excitonic lines agrees well with the values of localization energies 

of excitons to donor centers. For wider ZnO wells the quantum confined Stark effect shifts the 

PL spectra below the band gap of ZnO. This is a direct consequence of the very large built-in 

electric field developed in ZnO/ZnMgO QWs grown along the polar c-direction. 

Acknowledgement: Work supported in part within European Regional Development Fund, 

through grant Innovative Economy (POIG.01.01.02-00-008/08). 

84

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Electronic structure of CdTe/PbEuTe/CdTe 

B.A. Orlowski 1 , S. P. Dziawa 1 , A. Reszka 1 , K. Gas 1 , S. Mickievicius 2 , S. Thiess 3 , 

W. Drube 3 . 

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Top part of the semiconductor nanostructure CdTe/Pb0.95Eu 0.05Te/CdTe with Pb0.95Eu 0.05Te 

buried under thin layer of CdTe (the layer transparent for part of photoemitted electrons) was 

studied with application of High Energy X-ray Photoemission Spectroscopy. The Energy 

Distribution Curves (EDC) corresponding to the valence band and core levels electrons of the 

buried layer and top cover CdTe layer were measured with application of synchrotron 

radiation of high energy h = 3510eV to obtain big escape depth of electrons photoemitted 

from buried layer. The measured peaks corresponding to the buried layer atoms were 

observed in the valence band region and in the high binding energy region for core levels 

Pb4f, Pb3d and Eu 3d. For top cover layer the contribution of valence band, Cd4d and 

Cd3d core levels were obtained. Measured Te4d, Te 3d and Te4d spectra possesses 

contribution as well from buried as from the top cover layer. 

The nanostructure was grown by MBE deposition method in the Institute of Physics, Polish 

Academy of Sciences in Warsaw [1]. The CdTe buffer layer was evaporated on GaAs wafer 

and Pb0.95Eu0.05Te layer of 6nm thick, evaporated on it. The layer of Pb0.95Eu 0.05Te was 

covered by CdTe layer of thickness 22 nm. The structure was exposed to the air and 

photoemission spectra were performed ex situ using the Tunable High Energy X-ray 

Photoemission Spectrometer at HASYLAB, Hamburg [2]. After sputtering of CdTe top layer 

the photoemission signal of buried layer elements remarkably increases (see Fig.1, Pb5d). 

Main parameters of the electronic structure of CdTe/Pb0.95Eu 0.05Te/CdTe were determined. 

Intensity [a. u.] 

1 . 4 

1 . 2 

1 . 0 

0 . 8 

0 . 6 

0 . 4 

0 . 2 

0 . 0 

C d T e / P b E u T e / C d T e 

H I G H E N E R G Y X P S 

h ν = 3 5 1 0 e V 

S p u t t e r i n g 

2 n d 

1 s t 

n o 

v b 

C d 4 d 

P b 5 d 

T e 4 d 

- 1 0 0 1 0 2 0 3 0 4 0 5 0 

B i n d i n g E n e r g y [ e V ] 

Fig.2. Set of EDC’s of the valence band, Cd4d, Pb5d and Te4d electrons region and measured after following 

steps of cleaning of the sample by sputtering CdTe 22nm top layer. 

The authors acknowledge support by MSHE of Poland research Projects DESY/68/2007 and by the European 

Community FP6 Programme "Integrating Activity on Synchrotron and Free Electron Laser Science" at DESY. 

1. M. Szot, L. Kowalczyk, E. Smajek, V. Domukhovski, J. Domagała, E. Łusakowska, B. Taliashvili, 

P. Dziawa, W. Knoff, W. Wiater, T. Wojtowicz, T. Story, Acta Phys. Pol. 114, 1397 (2009). 

2. Th. Eickhoff, V. Medicherla, W. Drube, Jour.Electr. Spectr.Rel. Phen. 137-140, 85-88 (2004) 

orbro@ifpan.edu.pl 

85 

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MoP48 _______________________________________________________________ 


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86

40th _______________________________________________________________ 


Multi-interface layered P-doped silicon structures for third generation 

photovoltaics 

Mikael Hosatte 1 , Marek Basta 1 , Bartłomiej S. Witkowski 2 , Zbigniew T. Kuznicki 

1 and Marek Godlewski 2 

1 Photonic Systems Laboratory, Pole Api, Blvd. Sebastien Brandt, 67414 Illkirch- 

Graffenstaden, France 

2 Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warszawa, 

Poland 

Nanoscale Si-layered systems represent an attractive way to enlarge optical and electrical 

functions in Si optoelectronic, photonic and PV technology. Physical interactions transform 

the initial Si material to a new Si-based metamaterial. The device architecture also plays a 

role in specific nonlinear features. The seemingly paradoxical behavior requires a better 

insight into understanding the mechanisms determining the macroscopic performance. We 

report here some specific optical and electrical properties resulting from the complexity of 

different test structures. Optoelectronic properties of nanostructured materials can differ 

greatly comparing to those of bulk, or even thin film. The complexity of low-dimensional 

interactions renders impossible to directly use the description of the phenomena developed for 

previous device generations [1]. This is particularly true for Multi-interface Novel Devices 

(MINDs) which results mainly from the superposition of a PN junction [2], a nanoscale 

system [3] and a multi-interface architecture. In MINDs, whose collection efficiencies have 

been improved since the first generation, the buried substructure is presented as a 

metamaterial layer because it exhibits physical properties different than bulk silicon. In 

particular, it allows low energy-carrier multiplication. 

a) b) 

Figure 1. Architecture of MIND test structure (a) and SEM measurement showing buried nanoscale 

substructure as well as metamaterial layer (b) 

[1]P. Havu, V. Havu, M.J. Puska, M.H. Hakala, A. Foster, and R.M. Nieminen, “Finiteelement 

implementation for electron transport innanostructures”,J.Chem. Phys.124, 054707 

(2006) 

[2]C.T Sah, R.N. Noyce, W. Shockley, Proc. IRE 45, 1228 (1957). (2001). 

[3]Z. T. Kuznicki, Multi-interface novel devices, model with a continuous substructure, “3 rd 

Generation Photovoltaics for High Efficiency through Full Spectrum Utilization”, ed. A. 

Luque& A. Marti (Institute of Physics Publishing, Bristol, UK, 2003) pp. 165-195. 

87

MoP50 _______________________________________________________________ 


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88

40th _______________________________________________________________ 


ZnO-based Nanotubes Obtained by the Oxidation of ZnTe 

and ZnTe/Zn Nanowires 

K. Gas 1* , E. Dynowska 1 , E. Janik 1 , A. Kami ska 2 , S. Kret 1 , J.F. Morhange 3 , 

I. Pasternak 4 , M. Wiater 1 , W. Zaleszczyk 1 , R. Hołyst 2 , E. Kami ska 4 , T. Wojtowicz 1 , 

W. Szuszkiewicz 1 

1 Institute of Physics PAS, Al. Lotników 32/46, Warsaw, Poland 

2 Institute of Physical Chemistry, PAS, ul. Kasprzaka 44/52, Warsaw, Poland 

3 Institut des Nanosciences de Paris, UMR 7588, UMPC, 4 Place Jussieu, Paris, France 

4 Institute of Electron Technology, Al. Lotników 32/46, Warsaw, Poland 

One-dimensional (1D) semiconductor nanostructures like, e.g., nanowires (NWs) or 

nanobelts recently attracted a great deal of attention due to their potential application in 

electronic and optoelectronic nanodevices. Among many materials ZnO is particularly 

intensively studied due to its wide, direct energy gap (3.37 eV at 295 K) and large exciton 

binding energy of 60 meV. The non-intentionally doped ZnO usually exhibits n-type 

conductivity and it is difficult to convert it to p-type. The lack of p-type ZnO is the major 

obstacle in possible device applications of this material. Contrary to ZnO, ZnTe can be 

relatively easy highly p-type doped. Moreover, as it was already shown thermal oxidation of 

nitrogen-doped ZnTe allows to obtain p-type ZnO [1], therefore one possible way to produce 

p-type, ZnO-based NW structure would be through the oxidation of p-type ZnTe NWs. In this 

paper we report a successful fabrication of the ZnO-containing nanotubes obtained by thermal 

oxidation. For this purpose MBE-grown ZnTe and ZnTe/Zn core/shell NWs were oxidized by 

annealing in flowing O2 gas using both a rapid thermal annealing apparatus and a furnace. 

Some samples were annealed in flowing Ar gas for a comparison. 

Scanning and transmission electron microscopy (SEM and TEM, respectively) 

demonstrated tubular character and some changes in the NWs’ morphology after the oxidation 

process. The TEM analyses also revealed that the nanotubes are built of small ZnO and TeO2 

crystallites with random crystallographic orientations. The average inner diameter of the 

nanotubes is about 40 nm whereas their outer diameter can reach up to 100 nm (measured in 

the central part of the NW). We determined the chemical composition of the samples using 

energy dispersive X-ray spectroscopy. Complementary information on the structure properties 

of the NWs was obtained by X-ray diffraction, the optical properties of the NWs were also 

investigated by Raman scattering. The influence of the technological conditions on the 

evolution of the nanostructures is shown and discussed. The results of our studies suggest that 

the most probable mechanism of formation of such tubular nanostructures consists of two 

major steps. Firstly, the ZnTe is partially decomposed by the reaction with oxygen both at the 

surface of the NW and along its axis at the center of the NWs. Due to very fast oxygen 

diffusion along the [111] direction a creation of a cavity starts in the central part of the NW. 

Next, the Zn from the surface produce the ZnO shell and the remaining Te aggregate into 

small nanocrystals, which decorate the hollow inner part of the ZnO NW [2] or (after an 

oxidation) form TeO2. 

The studies were partially supported by the European Union within European 

Regional Development Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08). 

* Corresponding author, e-mail address: kgas@ifpan.edu.pl 

[1] E. Prze dziecka et al., Semicond. Sci. Technol. 22, 10 (2007). 

[2] P. Lu, D.J. Smith, phys. stat. sol. (a) 107, 681 (1988). 

89

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Composition-dependentthermalresistanceofmultilayeredstructurestakingintoaccountphononreflection,scatteringandtunneling. 

DariuszŻak 1,2 ,WłodzimierzNakwaski 2 

1 InstituteofElectronTechnology, 

al.Lotników32/46,02-668Warsaw,Poland. 

2 PhotonicsGroup,InstituteofPhysics,TechnicalUniversityofLodz, 

ul.Wolczanska219,90-924Lodz,Poland. 

Abstract 

Developmentinthesynthesisandprocessingofnanoscaledevicescreatesthe 

demandtopredicttheirthermalproperties.Nowadays,superlatticestructures 

arebasecomponentsoflightemittingandlightdetectingdevicesinmiddleof 

infra-redspectrumrange.Thermalpropertiestakeimportantplaceindesigning 

process.Heatspreadinginmultilayersstructuresismuchdifferentthanthatin 

bulkmaterials.Mainpartofheattransportinthosestructures,isgovernedby 

thephonontransport.Thepresenceofmultipleinterfacesinmultilayerstructuresimpairssignificantlythephonontransportofheat,whichresultsinthe 

reducedthermalconductivitiesofthelayersandamountstoincreasedthermal 

resistivityofthedevices.Thebehaviourofthephonon/heattransportinthe 

presenceofinterfacesisachallengeinanalyticaldescription.Inthisarticlea 

semi-analyticalexpressionbasedontheacousticmismatchmodelandthediffuse 

mismatchmodelisproposed,thatpredictsthethermalconductivityofsuperlatticestructuresatroomtemperaturesaccurately.ThemodelwasusedtopredictthethermalconductivitiesofSi/Ge,Si/Si0.3Ge0.7.Si/Gesuperlatticestructuresconsistof60,80,100,200,300periodsandhavedifferentlayerssizeratio 

foreachsample.AllSi/Si0.3Ge0.7superlatticestructureswithperiodwidths 

300˚A,150˚A,75˚A,45˚Aare3µmthinkandhave2:1layerratio.Theobtained 

calculationsofthermalconductivityinrangeoftemperaturefrom200Kto300K 

areingoodagreementwiththeexperimentaldata.Thebehaviourofthermal 

conductivityinthepresentsofchangingnumbersofinterfacespredictedbythis 

modelisconfirmedbymeasurements. 

1 

90

40th _______________________________________________________________ 


Pb1-xGexTe surface with Sm 2+ and Sm 3 + doping 

A. Reszka 1 , B.A. Orlowski 1 , M.A. Pietrzyk 1 , A. Szczerbakow 1 , S. Mickievicius 2 , 

S. Balakauskas 2 , R.L. Johnson 3 

1 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, 

Poland 

2 Semiconductor Physics Institute, A. Gostauto 11, 2600 Vilnius, Lithuania 

3 Institut für Experimentalphysik, Universität Hamburg, Luruper Chaussee 149, 22761 

Hamburg, Germany 

In the present work we report the experimental results of resonant photoemission study 

of single crystal Pb1-xGexTe surface doped with Sm. Doping of IV-VI semiconductors with 

rare earth atoms turns these materials into diluted magnetic semiconductors, exhibiting 

a number of specific properties [1]. 

The main goals of the presented studies were: 

– Determination of Sm 4f electrons contribution to the valence band of Sm/Pb1-xGexTe. 

– Verification of Sm ions charge states (Sm 2+ and Sm 3+ ) to determine their structure 

and binding energies. 

– Investigation of the changes of Sm 2+ /Sm 3+ ratio during the process of Sm incorporation into 

the host lattice. 

The Pb1-xGexTe (x=0.03) samples were grown by the Bridgman method in the Institute 

of Physics Polish Academy of Sciences in Warsaw. The photoemission experiments were 

performed at the FLIPPER II beam line in HASYLAB in Hamburg, Germany. 

Typical feature of rare-earth photoemission spectroscopy (PES) is a characteristic 

behaviour of its intensity related to strongly localized 4f-shell electrons. Therefore, the PES 

investigations of Sm/Pb1-xGexTe were carried out for the varying photon energy through the 

region corresponding to Sm 4d 4f Fano resonance (h = 130-160 eV) [2]. In order to get 

a clean surface for experiment the sample was sputtered by Ar + ions to remove possible oxide 

contaminations and annealed at the temperature 300 ºC under UHV conditions. Samarium 

was deposited on the top of Pb1-xGexTe sequentially to obtain 1, 3 and 7 ML capping layers. 

Afterwards sample was annealed at 250 ºC for 0.5, 1.5 and 6.5 hours to incorporate Sm atoms 

into Pb1-xGexTe crystal matrix. After each deposition and annealing processes the set of 

energy distribution curves (EDC) spectra was measured. Deposited samarium ions occur as 

Sm 2+ and Sm 3+ at the surface. Annealing led to the decrease of Sm 2+ /Sm 3+ ratio indicating 

change in the interaction of Sm ions with their neighbourhood. 

The authors acknowledge support by MSHE of Poland research Projects DESY/68/2007 and by the 

European Community via the Research Infrastructure Action under the FP6 Structuring the European 

Research Area" Programme (through the Integrated Infrastructure Initiative "Integrating Activity on 

Synchrotron and Free Electron Laser Science") at DESY. Partially supported by Innovative Economy 

(POIG.01.01.02-00-108/09) and (POIG.01.01.02-00-008/08) 

[1] T. Story. Semimagnetic Semiconductors Based on Lead Chalcogenides. 

Lead Chalcogenides: Physics and Applications. Taylor & Francis, New York 2002. 

[2] U. Fano, Phys. Rev. B 23 (1961) 1866. 

91

MoP54 

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Studies of Optical Properties of Protonated Poliazomethine 

Thin Films 

H. Bednarski 1 , J. Weszka 1 , M. Domański 1 and V. Cozan 2 

1 Centre of Polymer and Carbon Materials, Polish Academy of Sciences, 34 M. 


2 Petru Poni Institute of Macromolecular Chemistry, Aleea Gr. Ghica Voda 41 A , 

700487 Iasi, Romania 

The poly(p-phenyleneazomethine) (PPI) belongs to alternately conjugated polymers 

revealing semiconducting properties, thus belonging to the family of organic semiconductors. 

PPI is isoelectronic counterpart of poly(p-phenylene-vinilene) (PPV), which is well 

known for its wide applications in organic optoelectronics. Having nearly the same π electron 

system as PPV [1], the PPI differ structurally in the presence of nitrogen atoms. This 

structural feature opens an additional way of chemical doping, by nitrogen atoms lone 

pair protonation. Doping of conjugated polymers is a well established way of influencing 

on important electronic, opto-electronic and mechanical properties of semiconducting 

polymers. 

Doping of poliazomethines is realized mainly based on acid chemistry. Such a technique 

makes the process complex and difficult to control. Apart from intentional protonation 

always exist possibility of occurrence of unwanted side reactions like hydrolysis, decomposition 

etc. [2]. Moreover, the routine experimental methods such as IR, UV-vis, provide 

only averaged quantities, thus microscopic details are not fully resolved. Generally, the 

microscopic mechanism of protonation of polyazomethines is not well understood and 

many reported results are unclear. 

The purpose of this work is twofold, namely experimental studies of optical properties 

of protonated poliazomethine thin films, as well as theoretical studies of protonation 

mechanism of this important group of materials. Performed theoretical calculations are 

aimed to rationalize observed experimental finding such as a red shift of the maximum of 

the absorption band due to protonation. 

[1] J. Weszka, H. Bednarski and M.Domanski, J. Chem. Phys. 131 (2009) 024901. 

[2] A. Iwan and D. Sek, Prog. Polym. Sci. 33 (2008) 289-345. 

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The reasons of destruction of nanoporous GaAs matrix 

fabricated by electrochemical etching 

A. V. Atrashchenko 1 , V. P. Ulin 1 , V. P. Evtikhiev 1 

1 Ioffe Physical-Technical Institute of the Russian Academy of Sciences, 

Politekhnicheskaya 26, 194021, St Petersburg, Russia 

The goal of the present study is to find out the reasons of the destruction of porous 

matrices based on n-type GaAs oriented in (100) created by using anodic electrochemical 

etchinganddefineparametersoftheporouslayers(poresdiameter, wallsthickness, depth, 

period of branching) for further application of such matrices in nanocomposite materials 

(matrixes with filled with metals or alloys (Ga, In, Ga-Au, In-Au)) [1,2]. 

Aperspectivetechniqueofcreatingsuchmatricesisthemethodofanodicelectrochemical 

etching which allows one to obtain nanoporous matrices on large areas. Experiments 

in [3,4] show that a creation of nanoporous matrices by electrochemical etching method 

meets with a problem of destruction of porous layer with the increasing of the etching 

depth. 

Based on previously obtained data [4] and carried out experiments in this paper there 

were suggested three hypotheses explaining the destruction of the porous layer with the 

increasing of depth. 1) During the etching occurs a catastrophic heating which leads to a 

change of the electrical parameters of the reaction. The temperature measurements made 

while executing every experiment has refuted this hypothesis. 2) There is a different speed 

of movement of the electrochemical reaction (relative to the front of etching) in different 

halides. To check this hypothesis we changed the electrolyte composition by leaving only 

one halide. This led to predictable changes in the pores parameters [5], but didn’t remove 

the problem of porous layer destruction. Occasionally we found that with the increasing 

of the pore size the undamaged layer depth increases. 3) Mechanical destruction of the 

porous layer is due to high pressure of products of the etching. In etching form the 

products whose volume is larger than etched volume. The products go outside through 

nanochannels. The increase of the nanochannel length leads to drastic amplification of 

resistance to the products outlet. At some moment a pressure of the etching products on 

a pore walls exceeds the value of the tensile strength so that the pressure at the front of 

pore formation is higher than one in the middle of the porous layer. This explains why 

at stopping of the etching, when the destruction starts, we can see the destruction only 

at the front of etching. 

We have defined the reason of the porous matrices destruction while increasing of the 

porous layer depth by anodic electrochemical etching which is a mechanical destruction 

of the pores walls due to amplification of the etching products pressure on the walls. 

We have defined the limits of the parameters variation for subsequent usage them as a 

medium for creation of nanocomposite metal-semiconductor A3B5 materials: the pores 

diameter is from 20 nm to 70 nm (up to 200 nm in fluoride electrolytes with an abrupt 

decrease of the structural order), the walls thickness lies within 10-20 nm, the depth of 

branching ranges from 150 nm to 1200 nm. We have outlined the methods allowing one 

to increase the porous layers depth by varying pulse current while etching. 

[1] J. B.Pendry, Phys. Rev. Lett. 85, 3966 (2000); 

[2] M. G. Silveirinha, C. A. Fernandes, Phys. Rev. B 78, 033108 (2008); 

[3] M. Christophersen et al., Phys. Stat. Sol. (a) 197, 197, (2003); 

[4] V. P. Ulin, S. G. Konnikov,Semiconductors 41, 832 (2007); 

93

MoP56 _______________________________________________________________ 


Effect of Substitution of Ti for Cd in CdCr2Se4 p-Type Semiconductor 

E. Malicka 1 , T. Groń 2 , A.W. Pacyna 3 , H. Duda 2 and J. Krok-Kowalski 2 





The CdCr2Se4 spinel combines the p-type semiconducting and ferromagnetic properties 

with Curie temperature TC = 142 K and Curie-Weiss temperature qCW = 190 K [1,2]. 

Magnetization of CdCr2Se4 reaches the full saturation of 5.98 µB per molecule [3]. The 

ferromagnetic properties of CdCr2Se4 are a result of dominating interactions between the 

nearest-neighbour chromium ions and of weaker superexchange couplings between the more 

distant chromium ones [4]. The Cr 2p XPS spectra of CdCr2Se4 showed the spin-orbit 

splitting between the final Cr 2p3/2 and Cr 2p1/2 states of 9.5 eV. The Cr 2p3/2 states are split 

into two peaks at 574.2 and 575.2 eV. The peak separation with the binding energy difference 

ΔE about 1 eV is typical of the 3d 3 elements with localized magnetic moment of 3 µB [5]. 

CdCr2Se4 crystallizes in the cubic structure (Fd3m). The X-ray refinements showed that the 

(Cd) ions have a preference to be located in the tetrahedral sites and the [Cr] ions prefer to be 

located in the octahedral sites of the spinel structure [6]. 

Chemical composition and structure refinement gave the sample composition and cation 

distribution according to the spinel formula: (Cd0.88Ti0.08)[Cr2]Se4. Magnetization, ac and dc 

magnetic susceptibility of (Cd0.88Ti0.08)[Cr2]Se4 were measured in the zero-field-cooled mode 

using a Lake Shore 7225 dc magnetometer/ac susceptometer at 4.3 K and in applied external 

magnetic fields up to 60 kOe, and a Faraday type Cahn RG automatic electrobalance in the 

temperature range 4.3-300 K and at 1 kOe and 2 kOe, respectively. 

The dc magnetic measurements of (Cd0.88Ti0.08)[Cr2]Se4 showed ferromagnetic order 

with Curie temperature TC = 129 K and Curie-Weiss temperature qCW = 138 K. Saturation 

magnetization of 4.73 µB/f.u. at 4.3 K and at 60 kOe seems to be strongly reduced in 

comparison with the CdCr2Se4 matrix. Such considerable lowering of magnetic moment 

induced by titanium substitution could be explained with only a transition of the certain 

number of Cr ions from the high-spin states to the low-spin states. Additionally, the ac 

magnetic measurements revealed a spectacular peak at 450 Oe and 1 kOe in the real part of 

the first harmonic susceptibility curve near TC, similar to the Hopkinson peak. Zero-value of 

its imaginary part below TC indicates a lack of the energy loss connected with the spin 

rearrangement processes. This is consistent with zero values of second and third harmonic ac 

susceptibility in the temperature range of 4.5-160 K, suggesting the lack of short-range 

magnetic interactions. 


[1] H.W. Lehmann, Phys. Rev. 163, 488 (1967). 

[2] P.K. Baltzer, H.W. Lehmann, and M. Robbins, Phys. Rev. Lett. 15, 493 (1965). 

[3] R.C. LeCraw, H. von Philipsborn, and M.D. Sturge, J. Appl. Phys. 38, 965 (1967). 

[4] P.K. Baltzer, M. Robbins, and P.J. Wojtowicz, J. Appl. Phys. 38, 953 (1967). 

[5] V. Tsurkan, St. Plogmann, M. Demeter, D. Hartmann, and M. Neumann, Eur. Phys. J. B 

15, 401 (2000). 

[6] T. Groń, A. Krajewski, J. Kusz, E. Malicka, I. Okońska-Kozłowska, A. Waśkowska, Phys. 

Rev. B 71, 035208 (2005). 

94

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Thermoelectric power in epitaxial Bi2Se3/Si(111) layers 

K. Dybko , M. Szot, T. Story and G. Karczewski, 

Institute of Physics, Polish Academy of Sciences, 

Al. Lotników 32/46, 02-668 Warszawa, Poland 

S. Schreyeck, C. Schumacher, K. Brunner and L.W. Molenkamp 

! " 

Bi2Se3 belongs to the class of three-dimensional topological insulators characterized 

by a bulk insulating state and conducting two-dimensional surface states with linear Diraclike 

dispersion. As grown Bi2Se3 samples are usually n-type due to inevitably present charged 

Se vacancies. Consequently, the conductivity of the system consists of parallel bulk and 

surface states conductivities. The observation of the surface states electrical properties 

requires minimalization of the bulk states contribution. It has been demonstrated in high field 

magnetotransport experiment [1] that beyond magnetic field corresponding to quantum limit 

for 3D carriers the clear Shubnikov de Haas oscillations of 2D character appear. This high 

field signature of surface states unambiguously proved the coexistence of both conducting 

channels in bulk samples. 

Here we study how the surface states affect thermoelectric properties of the whole 

electronic system in Bi2Se3. The samples were grown by molecular beam epitaxy on 

reconstructed (7x7)–(111) surface of Si semi-insulating substrate. Typically, samples are 100 

nm thick and have electron concentration of the order of 10 19 cm -3 . The Seebeck effect was 

measured over the temperature range of 10-300 K in ab-plane of the samples. The magnitude 

of the thermoelectric power decreases smoothly with lowering temperature until around 80 K, 

where it develops into a broad peak with maximum at 45-50 K. The absolute height of this 

peak is within 10 percent equal to the room temperature value (-60 V). The observed 

anomaly could be attributed to the theoretically predicted enhancement of the thermopower 

for surface states of topological insulators [2,3]. Here we measure the sum of individual 

contributions to the thermopower originating from bulk and surface states weighted by their 

electrical conductivities. Therefore, we also consider an alternative explanation that the 

effect is due to phonon drag, which may lead to the enhancement of the low temperature 

thermopower in semiconductors. 

[1] J.G. Analytis et al. , Nature Phys. 6, 960 (2010). 

[2] R. Takahashi and S. Murakami, Phys. Rev. B 81, 161302 (2010). 

[3] P. Ghaemi, R.S.K. Mong and J.E. Moore, Phys. Rev. Lett. 105, 166603 (2010). 

95

MoP58 

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Diamagnetism of the pre-paired electronic systems: 

the flow equation study 

M. Zapalska and T. Domański 

Institute of Physics, M. Curie Sk̷lodowska University, 20-031 Lublin, Poland 

Magnetic ordering of the electronic systems can originate from a variety of mechanisms. 

It can be explained for instance by the energetic reasons (Pauli paramagnetism), assigned 

to the orbital effects (diamagnetism) or to the mutual electron-electron interactions which 

through the exchange coupling induce either the ferromagnetic or antiferromagnetic order. 

Among these phenomena the particular version of ordering (perfect diamagnetism) 

appears whenever the Fermi liquid becomes unstable towards the electron pair formation 

and the system becomes superconducting. It is well known that superconductivity goes 

hand in hand together with the perfect diamagnetism (Meissner effect). In his seminal 

paper P.W. Anderson explained this in terms of the Anderson-Higgs mechanism when the 

phasal Goldstone mode is swallen producing the massive term A 2 . 

Recent studies of the Princeton group [L. Li et al, Phys. Rev. B 81, 054510 (2010) by 

means of the high-presission torque magnetometry reveiled that in cuprate materials the 

remarkable diamagnetic response survies to temperatures much higher than critical Tc. It 

is expected that apparantly the preformed electron pairs (which above Tc are not capable 

to establish the long-range coherence) are responsible for such residual diamagnetism. We 

shall analyze this problem using the nonperturbative flow equation technique designed 

within the numerical renormalization group scheme. 

96

40th _______________________________________________________________ 


Quantum Monte Carlo vs. Density Functional Methods for the prediction of 

relative energies of small Si-C clusters 

Nevill Gonzalez Szwacki and Jacek A. Majewski 

Faculty of Physics, University of Warsaw, ul Hoża 69, 00-681 Warszawa, Poland 

In many systems, prediction of the structural properties requires correct description of 

the electron correlation, clearly exceeding the accuracy of the available exchange correlation 

functionals in the density functional theory (DFT). This is also the case in small systems with 

very non-homogenous distribution of electronic charge, like for example Si–C clusters, which 

play an important role are in technological processes, such as chemical vapor deposition used 

for fabrication of SiC thin films. The simulation of the growth processes is out of scope of abinito 

methods and has to be done using effective approaches after ‘coarse graining’ procedure. 

The quality of the effective potentials is crucial for reliability of the predictions. Therefore, 

the effective potentials are usually fitted to the results of the first-principles calculations for 

building blocks of a material. 

Numerous experimental and theoretical studies have been performed to investigate 

equilibrium geometries, vibrational frequencies, and relative energies of small SinCm cluster 

isomers [1,2]. Most of the calculations employed standard approximations to the DFT. 

In order to examine the accuracy of various DFT exchange-correlation (XC) 

functionals in predicting the relative energies of cluster isomers and to provide new 

benchmark data, we have performed diffusion quantum Monte Carlo (DMC) calculations for 

small SinCm clusters. We compare our DMC results with DFT ones obtained using the local 

density approximation (LDA), Perdew-Burke-Ernzerhof generalized gradient approximation 

(GGA), and the popular B3LYP hybrid Hartree-Fock/DFT functional. On the basis of our 

DMC results for Si-C clusters, we conclude that LDA and GGA XC functionals are not 

reliable for predicting the relative stability of various isomers of covalent SiC clusters, 

B3LYP does a little bit better, and generally the errors of various methods are completely 

unsystematic. This is illustrated in Fig. 1, where we plotted the energy (relative to the 

average) of four SinCm isomers. In particular, it is easily seen that the LDA approximation 

underestimates the relative energy of the planar (1) and (2) clusters, whereas the GGA 

approximation is unable to capture correctly the relative energy of the 3D clusters (2) and (3). 

The present studies clearly demonstrate that 

the determination of the effective potentials 

on the basis of DFT calculations with 

approximated exchange-correlation 

functionals can be misleading and 

computational schemes going beyond this 

approximation are very desirable. 

This paper has been supported by the project 

“SiCMAT” (Innovative Economy, 

POIG.01.03.01-14-155/09-00) 

[1] M. Bertolus, F. Finocchi, and P. Millie, J. Chem. Phys. 120, 4333 (2004). 

[2] C. R. Hsing et al., Phys. Rev. B 79, 245401 (2009). 

97

MoP60 _______________________________________________________________ 


Analysis of a Spatial Hole Burning Effect in a Square and 

Triangular Lattice Photonic Crystal Laser 

Marcin Koba 1,2 , and Pawe̷l Szczepański 1,2 

1 Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland 

2 National Institute of Telecommunications, Szachowa 1, 04-894 Warsaw, Poland 

In this paper we present an approximate analysis of the nonlinear operation of the 

two-dimensional (2D) photonic crystal (PC) lasers taking into account nonlinear effects 

(gain saturation, spatial hole burning). 

Our analysis is conducted for the laser with an active medium that is confined in 

the square region with circular holes arranged in square or triangular Bravais’ lattice. 

The analysis is based on two-dimensional coupled wave equations [1]-[4] for TE and TM 

modes, modified by introduction of nonlinear gain and energy theorem developed earlier 

forvarioustypesoflaser[5], includingDFBstructures[6]-[8]. Similarly, aswehavedonein 

e.g. [6]-[8] the field distributions appearing in the energy theorem (including nonlinearity) 

were approximated by those existing in the linear structure (i.e. at threshold). 

Following our derivation presented in [4],[9],[10] we introduce an approximate equations 

describing the small signal gain coefficient α0 as a function of system parameters, 

where we have introduced power saturation and spatial hole burning effects. We use these 

equations to calculate laser characteristics illustrating hole burning effect impact on cw 

operation of square and triangular lattice PC laser structure above the threshold. With 

thehelpofthepresentedtechniqueitispossibletocalculatetheoptimalcouplingstrength 

providing maximal power efficiency of the given 2D photonic laser structure. 

[1] K. Sakai, E. Miyai, and S. Noda, Opt. Express 15, 3981 (2007). 

[2] K. Sakai, E. Miyai, and S. Noda, IEEE J. Quantum Electron. 46, 788 (2010). 

[3] K. Sakai, J. Yue, and S. Noda, Opt. Express 16, 6033 (2008). 

[4] M. Koba, P. Szczepanski, and T. Kossek, IEEE J. Quantum Electron. 47, (13) 2011. 

[5] L. Wosińska, P. Szczepański, and W. Woliński, Opto-Electron. Rev. 1, 26 (1992). 

[6] R. Paszkiewicz, A. Tyszka-Zawadzka, and P. Szczepański, Opt. Commun. 270, 314 

(2007). 

[7] P. Szczepański, D. Sikorski, and W. Woliński, IEEE J. Quantum Electron. 25, 871 

(1989). 

[8] P. Szczepanski, Appl. Opt. 24, 3574 (1985). 

[9] M. Koba, and P. Szczepanski, IEEE J. Quantum Electron. 46, 1003 (2010). 

[10] M. Koba, T. Osuch, and P. Szczepanski, J. Mod. Opt. submited for publication. 

98

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors TuI1 

Optical control of one and two spins in interacting quantum dots 

Alex Greilich, Samuel G. Carter, Danny Kim, Allan S. Bracker and Daniel Gammon 

Naval Research Laboratory, Washington DC 20375, USA 

The interaction between two quantum bits enables entanglement, the two-particle 

correlations that are at the heart of quantum information science. In semiconductor quantum 

dots much work has been focused on demonstrating single spin qubit control using optical 

techniques. However, optical control of two spin qubits remains a major challenge for scaling 

to a full-fledged quantum information platform. Here we combine advances in verticallystacked 

quantum dots with ultrafast laser techniques to achieve optical control of the 

entangled state of two spins. 

We demonstrate ultrafast optical control of two interacting electron or hole spins in 

two separate QDs using optical initialization, single-qubit gates with short pulses, and twoqubit 

gates with longer pulses or through precession in the exchange field. Local 

entanglement between the two spins is inferred from the coherent evolution of superposition 

states as measured in Ramsey fringes. 

The two-qubit gate speeds achieved here are over an order of magnitude faster than in 

other systems. These results demonstrate the viability and advantages of optically controlled 

quantum dot spins for multi-qubit systems. 

[1] Danny Kim, Samuel G. Carter, Alex Greilich, Allan S. Bracker and Daniel Gammon, 

Nature Physics 7, 223 (2011).�� 

99

TuI2 _______________________________________________________________ 


Graphene Transport Properties� 

Shaffique Adam 

Center for Center for Nanoscale Science and Technology, National Institute of Standards and 

Technology 

Arguably, one of the most intriguing properties of graphene transport is the nonvanishing 

``minimum conductivity” at the Dirac point. The carrier density in these single 

monatomic sheets of carbon can be continuously tuned from electron-like carriers for large 

positive gate bias to hole-like carriers for negative bias. The physics close to zero carrier 

density (also called the intrinsic or Dirac region), is now understood to be dominated by 

fluctuations in local disorder potential, breaking the landscape into puddles of electrons and 

holes [1]. I will discuss the competing effects of disorder, electron-electron interactions, and 

quantum interference on graphene’s transport properties and demonstrate that, remarkably, a 

semi-classical effective medium theory captures the physics in the experimentally relevant 

regime [2]. Figure 1 shows a comparison of our theoretical predictions [3] with subsequent 

experimental data from Columbia, Manchester, Maryland and Exeter universities showing 

good agreement. To further test the range of validity of our model, I compare our results to a 

fully quantum-mechanical numerical calculation [4] of the conductivity and find that while 

the two theories are incompatible at weak 

disorder, they are compatible for strong 

disorder. Armed with this success, I will 

discuss how future graphene experiments 

could shed light on some long-standing 

open questions in condensed matter 

physics. 

Figure 1: Comparison of the self-consistent 

theory [3] with experimental data from 

various groups around the world. (See Ref. 

[2] for details). Solid blue line shows the 

Dirac point conductivity for graphene in 

the presence of charged impurities of 

concentration nimp. The dashed line shows the quantum mechanical ballistic result 4e 2 /�h. 

Early results claimed that the conductivity was universal with a value of 4e 2 /h (dotted line). 

References: 

[1] S. Das Sarma, S. Adam, E. H. Hwang, E. Rossi, “Electronic transport in two dimensional 

graphene”, arXiv:1003.4731, Rev. Mod. Phys. (in press). 

[2] S. Adam, “Graphene carrier transport theory”, invited book chapter for Graphene 

Nanoelectronics: metrology, synthesis, properties and applications (Springer book series on 

nanoscience and technology). 

[3] S. Adam, E. H. Hwang, V. Galitski, and S. Das Sarma “A self-consistent theory for 

graphene transport” Proc. Nat. Acad. Sci. USA 104, 18392 (2007). 

[4] S. Adam, P. W. Brouwer, and S. Das Sarma “Crossover from quantum to Boltzmann 

transport in graphene” Phys. Rev. B Rapid Communications 79, 201404 (2009). 

100

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors TuI3 

Theoretical search for non-Abelian statistics in fractional quantum Hall states 

Arkadiusz Wójs 

Institute of Physics, Wroc�aw University of Technology, Wroc�aw, Poland 

Convincing demonstration of non-Abelian anyon quantum statistics (corresponding to 

the multi-dimensional realization of the braid group, allowed in two spatial dimensions) is a 

major challenge in today’s condensed matter physics. Promising physical systems for this 

quest are sought among correlated many-electron states a high magnetic field, responsible for 

the fractional quantum Hall effect at such Landau level fillings as �=5/2 or 12/5. In particular, 

the 5/2 state is believed to realize a superfluid condensate of p-paired “composite fermions” 

(electrons binding vortices of the many-body wave function) in an effectively compensated 

magnetic field. This hypothetical state, described by the “Pfaffian” wave function of Moore 

and Read, supports elementary charge excitations in form of fractional (e/4) quasiparticles 

which obey non-Abelian anyon quantum statistics. Anticipation of the Pfaffian ground state 

relies mostly on numerics, and it is confronted with rather ambiguous experimental evidence, 

including recent reports of the (unexpected) depolarization of spin at �=5/2. Therefore, the 

focus of this talk will be on available evidence concerning Pfaffian dynamics (more generally, 

non-Abelian quantum statistics) in realistic conditions of the fractional quantum Hall effect. 

We will begin by revisiting the question of spin polarization at �=5/2. The combination 

of exact diagonalization and quantum Monte Carlo in spherical geometry confirms quantum 

ferromagnetism in clean systems, as expected for the Pfaffian phase, but also reveals stability 

of Skyrmions (topological spin excitations) in sufficiently thick systems [1]. As pairing nature 

of the ferromagnetic (Pfaffian) ground state implies that Skyrmions at �=5/2 carry twice the 

charge (e/2) of spinless quasiparticles, the (realistic) lateral disorder aids Skyrmion formation, 

in turn leading to local depolarization – in agreement with its photoluminescence signatures. 

Having established the role of spin we will confine further analysis to the spin-polarized 

channel and turn to the question of adiabatic connection (i.e., essential equivalence) between 

the exact Pfaffian state and the realistic Coulomb ground state. The problem is subtler than at 

�=1/3 (where the famous Laughlin wave function is firmly established), because of a longer 

correlation length, a more fragile gap, and a competition between two- and three-body effects 

(the Pfaffian state being a unique zero-energy ground state of the contact triplet repulsion). 

Since the analysis of overlaps or pair correlation functions computed in the largest tractable 

systems is hardly conclusive, we studied features linked directly to the non-Abelian statistics. 

Specifically, in addition to the neutral boson pair-pair collective mode with the characteristic 

roton dispersion, the Pfaffian ground state should have a neutral fermion excitation associated 

with an unpaired particle (analogous to the Bogoliubov-deGennes excitation of a conventional 

superconductor). In the relevant weakly paired phase, the neutral fermion dispersion should 

have a minimum near the Fermi wave vector. More importantly, the neutral fermion mode is 

predicted to become gapless in the presence of distant quasiparticles – as a consequence of 

their non-Abelian statistics within the Ising model with degenerate fusion channels (1 and �). 

Our calculations confirm [2] these qualitative features, in support of exotic statistics at �=5/2. 

Other issues will include Pfaffian/anti-Pfaffian duality, effects of Landau level mixing 

(e.g., on particle-hole symmetry) [3], and the pairing transition of composite fermions [4]. 

[1] A. Wójs, G. Möller, S. H. Simon, and N. R. Cooper, Phys. Rev. Lett. 104, 086801 (2010). 

[2] G. Möller, A. Wójs, and N. R. Cooper, http://arxiv.org/abs/1009.4956 

[3] A. Wójs, C. T�ke, and J. K. Jain, Phys. Rev. Lett. 105, 096802 (2010). 

[4] A. Wójs, C. T�ke, and J. K. Jain, Phys. Rev. Lett. 105, 196801 (2010). 

101

TuI4 _______________________________________________________________ 


Polariton condensation in dynamic acoustic lattices 

D. Krizhanovskii 1 , E. Cerda-Méndez 2 , M.Wouters 3 , K. Biermann 3 , K.Guda 1 , R.Bradley 1 , 

D.Sarker 1 , P. V. Santos 3 , R. Hey 3 and M. S. Skolnick 1 

1 Department of Physics and Astronomy, University of Sheffield, Sheffield, United Kingdom 

2 Paul-Drude-Institut für Festkörperelektronik, Berlin, Germany 

3 ITP, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland 

Microcavity polariton condensates 

arising either from Bose-Einstein condensation 

(BEC) or from Optical Parametric Oscillation 

(OPO) exhibit collective superfluid-like 

behavior [1](OPO), spatial and temporal 

coherence (OPO, BEC) and vortices (OPO, 

BEC). Here, we study spatial coherence of 

OPO polariton condensates formed by 

polariton-polariton scattering from the pump in 

external periodic potentials created by Surface 

Acoustic Waves (SAW)[2]. The effect of 

strong polariton-phonon coupling results in 

modulation of the polariton dispersion with 

marked formation of Brillouin zones of period 

k=π/λSAW and energy stop band widths up to ~0.5 

meV (Fig.1a). 

Without SAW the OPO “signal” condensate 

is formed at k=0 above threshold with a coherence 

length of about ~20-25 µm. As the height of the 

SAW potential is increased we observe dramatic 

reduction of the spatial coherence length (Ly) along 

the SAW direction by a factor of 3-4 (Fig.1c), a result of suppressed tunnelling between the 

adjacent SAW minima. A smaller decrease of the coherence length Lx by a factor of 2 

perpendicular to the SAW direction (Fig.1d) is attributed to the increased phase fluctuations, 

predicted theoretically for 1D system of the non-equilibrium OPO. The observed effect 

corresponds to transition from condensate to insulator state. Nevertheless, this is not a Mott 

insulator: the number of particles per potential well is still large compare to the case of 

superfluid-to Mott-insulator transition in cold atom system. Interestingly, at intermediate SAW 

powers the emission peaks at the edges of the 1 st Fig.1 a) Dispersion of polaritons subject to SAW 

potential. b) Image of condensate emission c)-d) 

Spatial coherence length of OPO signal parallel 

(LX) and perpendicular (LY) SAW at different 

pump powers. 

Brillouin zone (Fig.1b), indicating a phase 

difference of π between adjacent condensates. A likely reason for this is an additional scattering 

mechanism between the main pump beam and its diffraction replica. 

By contrast, inter-particle interactions at high densities screen the acoustic potential, 

partially reversing its effect on spatial coherence. Figs.1 c)-d) shows that with increasing 

excitation power the reduction of spatial coherence lengths occurs at higher SAW powers, thus 

indicating efficient screening of SAW potential at low acoustic powers as the polariton density 

is increased. 

Our work on polariton condensation in acoustic lattices provides new technology to 

investigate fundamental effects in hybrid light-matter system, such as coherent transport of 

condensates, creation of entangled states and Josephson tunneling. 

1. A. Amo, et al, Nature 457, 291 (2009) 

Ly (P =140 mW) 

laser 

40 

Ly (P =200 mW) 

laser 

Ly (P =240 mW) 

laser 

30 

Ly (P =300 mW) 

laser 

-5 0 5 10 15 

0 5 10 15 

2. E. A. Cerda-Méndez, D. N. Krizhanovskii et al, Phys. Rev. Lett. 105, 116402 (2010) 

102 

Energy (eV) 

1.5365 

1.5360 

1.5355 

1.5350 

1.5345 

1.5340 

1.5365 

1.5360 

1.5355 

1.5350 

1.5345 

1.5340 

a) 

b) 

-2 -1 0 1 2 

k-vector ky 

c) 

d) 

Ly (P laser =68 mW) 

SAW power (dBm) 

50 

20 

10 

0 

40 

30 

20 

10 

0 

Coherence length L y (µm) 

Coherence length Lx (µm)

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors TuO1 

Resonant Terahertz Absorption by Magnetoplasmons 

in Grating-Gate GaN/AlGaN-based Field-Effect Transistors 

K. Nogajewski 1 , K. Karpierz 1 , M. Grynberg 1 , W. Knap 2 , R. Gaska 3 , 

J. Yang 3 , M. S. Shur 4 , and J. ̷Lusakowski 1 

1 Faculty of Physics, University of Warsaw, ul. Ho˙za 69, 00-681 Warsaw, Poland 

2 CNRS - Université Montpellier2, Pl. E. Bataillon, 34095 Montpellier, France 

3 Sensor Electronic Technology, Inc., Columbia, South Carolina 29209, USA 

4 Rensselaer Polytechnic Institute, Troy, New York 12180, USA 

An interest to fabricate voltage-tunable detectors of THz radiation based on plasma 

excitations in field-effect transistors (FETs) is marked by an effort to test new types of 

structures and new materials. High electron mobility FETs based on GaN/AlGaN heterostructures 

offer a possibility of high-voltage/high-current THz applications in agressive 

environments. However, to support technical developments, basic physical investigation 

must be carried out on technologically advanced devices. 

The goal of the present work is to describe magnetoplasmon excitations in a twodimensional 

electron gas in a GaN/AlGaN heterostructure. Our experiments were carried 

out on samples that have been recently shown to exhibit gate-voltage tunable plasmon 

resonances at zero magnetic field (B) [1]. The samples were large-area (about 

1.6 mm×1.6 mm) FETs with the gate electrode composed of two interdigitated comb-like 

structures. Five transistors with the gate periodicity between 1.5µm and 4µm were processed 

on a high-quality GaN/AlGaN heterostructure. The metal grating served both as 

a gate electrode controlling the concetration of a two-dimensional electron gas (n) and as 

a coupler between magnetoplasmons and incident THz radiation. 

Transmission ( a.u. ) 

ν FIR = 2.52THz 

−3.5 −3 −2.5 −2 −1.5 −1 −0.5 0 

Gate Voltage ( V ) 

B = 8T 

B = 6T 

B = 4T 

B = 2T 

B = 0T 

Fig. 1: Transmission of 2.52 THz radiation 

through a GaN/AlGaN FET as a function of 

VG and B. Minima correspond to magnetoplasmon 

resonances. 

Bothmagnetoresistanceand magnetotransmission 

measurements were carried 

out at 4.2 K and B up to 10 T as a function 

of the gate polarization (VG). Shubnikov-de 

Haas oscillations of the magnetoresistance 

allowed us to estimate n as 

a function of the gate polarization (VG) 

and then an n-dependent electron quantum 

relaxation time τ. We found that τ 

dependsinanon-monotonicwayonnand 

ranges from 0.03 ps to about 0.1 ps. 

An example of magnetotransmission 

data shown in Fig. 1 gives a clear evidenceofexcitationofmagnetoplamonresonances 

tunable by B and VG. Magnetoplasmons 

frequency, ωmp, can only approximately 

be described by a classical 

formula ωmp = � 

ω2 c +ω2 p. Deviations 

from this dependence are explained as a result of interaction of plasmons in gated and 

ungated parts of the transistor channel. 

This work was partially supported by the JU ENIAC MERCURE project No. 220120. 

[1] A. V. Muravjov et al., Appl. Phys. Lett. 96, 042105 (2010). 

103

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Structural and electronic properties of functionalized graphene 

Karolina Milowska, Magdalena Birowska, and Jacek A. Majewski 

Faculty of Physics, University of Warsaw, ul. Hoża 69, PL-00-681 Warszawa, Poland 

We present extensive ab initio studies in the framework of the density functional theory 

(DFT) of graphene layers functionalized with simple molecules, which provide novel 

predictions for electronic structure of the functionalized graphene mono- and bilayers. The 

calculations reveal that the functionalization of graphene by simple molecules (e.g., such as 

OH, NH, and COOH) causes opening of the electronic band gap, just indicating new 

perspectives for design of field effect transistors (FETs) based on single and bilayer graphene. 

Remarkable electronic, mechanical and thermal properties of graphene have made it a 

promising candidate for a new generation of electronic devices [1]. However, the single and 

bilayer graphene have zero energy band gaps. Therefore, it hinders direct application of these 

systems in FETs. On the other hand, the functionalization of the graphene could change its 

electronic structure. Since quantitatively this effect is rather unknown, we have undertaken 

theoretical studies of this issue. 

In the present paper, we study the effects of functionalization of graphene with simple 

organic molecules (NHn, OH, and COOH) focusing on the stability and band gaps of the 

structures. We perform DFT calculations for graphene supercells with various numbers of the 

attached molecules. Employing the numerical package SIESTA, we completely optimize the 

geometry of the structures getting very good agreement with existing experimental data [2], 

and other theoretical calculations [3]. All studied groups bind covalently to the graphene layer 

implying sp 2 to sp 3 rehybridization and local deformation of the graphene plane. As example 

of our results, below we depict band 

structures of graphene layer 

functionalized with one single 

molecule per 3x3 graphene 

superlattice. The molecules are (a) - 

OH, (b) - NH, (c) – NH2, and (d) – 

COOH. The red dotted lines indicate 

band structure of pure graphene, the 

black ones the electronic structure of 

functionalized graphene. In all cases, 

the zero band gap at K-point of pure graphene opens, being equal to 0.11, 0.12, 0.25, and 0.24 

eV for OH, NH, NH2, and COOH, respectively. Generally, the stability of the functionalized 

graphene layers decreases with the growing concentration of functionalizing molecules. 

Interestingly, for higher (1x1) concentrations of OH, we observe separation of O and H, 

which cover now other sides of the graphene layer. On the other hand, quite naturally, the 

band gap increases with the concentration of the attached molecules, e.g., in the case of 2x2 

cell functionalized with hydroxyl group (graphene’s surface is strongly bent), the band gap 

reaches 1.04 eV. All this shows clearly that the band gap of graphene layers can be tuned 

within fairly large range. Further, it turns out that the functionalized graphene layers exhibit 

magnetic moments, just implying some possible spintronic applications. 

This paper has been supported by the project “SiCMAT” (Innovative Economy, POIG.01.03.01-14-155/09-00). 

1. S. Park, and R. S Ruoff, Nature Nanotech., 4, 217 (2009). 

2. H. B. Su, R. J. Nielsen, A. C. T. van Duin, and W. A. Goddard, Phys. Rev. B 75 134107 (2007). 

3. Jia-An Yan, M. Y. Chou, Phys. Rev. B 82 125403 (2010). 

104

40th _______________________________________________________________ 


Analysis of the magnetic anisotropy in ultrathin GaMnAs 

O. Proselkov 1 , W. Stefanowicz 1 , S. Dobkowska 1 , J. Sadowski 1,2 , 

T. Dietl 1,3 , M. Sawicki 1 

1 Institute of Physics, Polish Academy of Sciences, Warszawa, Poland 

2 MAX-Lab, Lund University, Lund, Sweden 

3 Institute of Theoretical Physics, University of Warsaw, Poland 

(Ga,Mn)As is the main test-bed material for testing concepts of future spintronics devices 

and its magnetic anisotropy is assumed to be reasonably well known both on the ground of 

understanding of the experimental data and on the level of a description its microscopic 

origins. However, some very recent studies have brought new insights into the magnetic 

anisotropy of thin and ultrathin (Ga,Mn)As. Firstly, in very thin (Ga,Mn)As layers, despite an 

adequate high Mn concentration to assure their homogenous metallic character, a blocked 

superparamagnetic response has been found [1]. Then, it was postulated that the strength of 

the ever-present in-plane uniaxial magnetic anisotropy was related to nanometer-scale ripples 

on the (Ga,Mn)As surface [2]. Furthermore, a collapse in the magnitude of the anomalous 

Hall effect was found for thin layers at low temperatures [3]. Finally, a cycloidal spin 

arrangement and the accompanying uniaxial in-plane anisotropy of diagonal [110]/[1-10] 

directions was suggested to form in very thin layers [4]. 

As all these findings indicate that the long celebrated macrospin approach [5] to the 

phenomenological description of the magnetic anisotropy may cease its validity in ultrathin 

layers, an examination of the conditions of its applicability in this technological important 

case is timely and important. Simultaneously, means for assessment of the abovementioned 

concepts are to be defined and tested. For these purposes we investigate in greater detail 

temperature dependence of the magnetic anisotropy of 4 nm Ga0.925Mn0.075As, a layer that 

according do [1] exhibits two types of magnetic responses: a temperature reversible one 

typical for a long-range-coupled magnetization and an irreversible one possessing 

characteristics similar to a blocked superparamagnet. We find that we can self consistently 

describe our findings on the grounds of the macrospin model as in [5] only above a 

temperature at which signatures of blocked superparamagnetic response disappears (25 K in 

this case). Below, the same model yields conflicting results which depend on the magnetic 

history of the sample. However, if applied at this temperature range, this approach implies 

disappearance of magnetic anisotropy at temperatures corresponding to the mean blocking 

temperature of the superparamagnetic part of the layer and a change of sign of the cubic 

anisotropy at the lowest temperatures. The last findings point to a strong coupling between 

these two major constituencies of the magnetic response in such a layers. 

The work was supported in part by the European Research Council through the FunDMS 

Advanced Grant within the "Ideas" 7th Framework Programme of the EC, EC Network 

SemiSpinNet (PITN-GA-2008-215368) and Polish MNiSW 2048/B/H03/2008/34 grant. 

[1] M. Sawicki, et al., Nature Phys. 6, 22 (2010); S. Dobkowska, et al., this conference. 

[2] S. Piano, et al., arXiv:1010.0112. 

[3] D. Chiba et al., Phys. Rev. Lett. 104, 106601 (2010). 

[4] A. Werpachowska and T. Dietl, Phys. Rev. B 82, 085204 (2010). 

[5] K.-Y. Wang, et al., Phys. Rev. Lett., 95, 217204 (2005). 

105

TuO4 _______________________________________________________________ 


Spin-lattice relaxation of a single Mn 2+ ion in a CdTe quantum dot 

M. Goryca 1,2 , P. Plochocka 2 , P. Wojnar 3 , T. Kazimierczuk 1 , M. Potemski 2 

and P. Kossacki 1,2 

1 Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland 

2 Grenoble High Magnetic Field Laboratory, CNRS, Grenoble, France 

3 Polish Academy of Sciences, Warsaw, Poland 

From the point of view of miniaturization of magnetic memory devices a quantum dot 

(QD) containing a single magnetic impurity is an interesting system. It has been demonstrated 

that it gives unique possibility to read and manipulate the electronic spin state of the single 

atom [1-3]. Although principles of using such system as a memory device are known, further 

studies of interaction of the magnetic ion with its neighborhood are still needed. Particularly a 

detailed knowledge about the spin-lattice relaxation is of a great importance, as this kind of 

relaxation is a main factor limiting the information storage time. 

In this work we present spectroscopic studies of the spin-lattice relaxation of a single 

Mn 2+ ion embedded in a CdTe/ZnTe QD, performed in high magnetic field. The experiment 

was done in a micro-photoluminescence setup at temperature of about 15 K. The magnetic 

field up to 12 T was produced with a superconductive magnet and applied in the Faraday 

configuration, parallel to the growth axis of the sample. The sample contained a single layer 

of self-assembled QDs. The PL of the QDs was excited using a tunable dye laser in the range 

570−610 nm. The spin-conserving excitation transfer between two QDs [4] was used to inject 

spin-polarized excitons into the QD containing the Mn 2+ ion and to orient its spin [3]. 

The spin-lattice relaxation time of the Mn 2+ ion was determined in two independent 

experiments. In the first one we measured the efficiency of the optical orientation of the Mn 2+ 

ion [3] as function of excitation power and magnetic field. Thus we were able to examine in 

detail the competition between two processes: the optical orientation of the Mn spin by spinpolarized 

excitons injected into the QD and thermalization of the magnetic ion in external 

magnetic field caused by spin-lattice relaxation. When these processes exactly compensate 

each other, i.e. the spin orientation rate is exactly equal to the relaxation rate, then the Mn 2+ is 

completely depolarized. Thus the spin orientation rate can be estimated using the exciton 

injection rate to the QD and probability of the Mn spin flip per one exciton [3]. 

In the second, time-resolved experiment we measured directly the Mn spin relaxation 

time. We used the same mechanism as previously to orient the magnetic ion. Once it reached 

the steady state we turned the excitation off for a certain period. Then we turned the excitation 

on again to probe the Mn spin. By varying the length of the dark period in the range of 20 ns – 

500 µs we were able to measure the relaxation time in the wide range of magnetic fields. 

Both experiments gave the same results within experimental accuracy. The spin-lattice 

relaxation time of the Mn 2+ ion in the QD for low magnetic field (around 1 T) reaches 

hundreds of microseconds and is comparable to the value measured for bulk, diluted 

(Cd,Mn)Te material [5]. It is, however, decreasing rapidly for high magnetic field and at 12T 

reaches value of tens of nanoseconds, which is over two orders of magnitude smaller than the 

one observed for bulk material. Possible origins of this surprising difference include strain 

fields, usually high in structures containing QDs. 

[1] L. Besombes et al., Phys. Rev. Lett. 93, 207403 (2004). 

[2] C. Le Gall et al, Phys. Rev. Lett. 102, 127402 (2009). 

[3] M. Goryca et al, Phys. Rev. Lett. 103, 087401 (2009). 

[4] T. Kazimierczuk et al, Phys. Rev. B 79, 153301 (2009). 

[5] T. Strutz et al., Phys. Rev. Lett. 68, 3912 (1992). 

106

40th _______________________________________________________________ 


Magnetophotoluminescence of CdTe/ZnTe Quantum Dots: 

G-factor and Diamagnetic Shift Variation in a Single Dot 

Tomasz Kazimierczuk 1 , Mateusz Goryca 1,2 , Piotr Wojnar 3 , 

Andrzej Golnik 1 , Piotr Kosacki 1,2 

1 Institute of Experimental Physics, Faculty of Physics, 

University of Warsaw, ul. Hoża 69, PL-00-681 Warsaw, Poland 

2 LNCMI-CNRS (UJF, UPS, INSA), BP 166, 38042 Grenoble Cedex 9, France 

3 Institute Physics, Polish Academy of Science, 

Al. Lotników 32/46, PL-02-668 Warsaw, Poland 

Typically, self-assembled quantum dots (QDs) are characterized by strong confining 

potential, which defines carrier wavefunctions. A flat shape of such QDs lifts the degeneracy 

between light and heavy holes in favor of the latter ones. Due to the selection rules, the 

recombination occurs between an electron and a hole of opposite spin directions. Thus, in the 

magnetic field along growth direction, all transitions with carriers in the ground state exhibit 

Zeeman given by a difference between electron and hole Landé factors. Particularly, the same 

Zeeman splitting should be observed for X, X + , X - , and XX transitions. Such a predictiction 

was tested already in early stages of QD research demonstrating equality between Landé 

factors for neutral and charged exciton with precision better than 1% [1]. 

In this work we present a comparison of magnetic field influence on various excitonic 

transitions in single CdTe/ZnTe QDs. The experiments included PL measurements in 

magnetic field up to 28T applied either 

perpendicular or parallel to the growth direction. 

Recorded data allowed us to extract two basic 

parameters: excitonic Landé factor related to linear 

Zeeman effect and diamagnetic shift related to 

quadratic field dependence. Contrary to the picture 

described previously, we discovered a clear 

systematic difference between g-factors inferred 

from X, X + , and X - transitions in Faraday 

configuration (Fig. 1). Landé factor inferred from 

the XX transition follows exactly values related to 

X transition, as in both cases the spectral effect is 

related to splitting of the same state (being final or 

initial one respectively). The average difference 

between X + and X - g-factors yields 21%. 

Similar but smaller difference between g-factors inferred from different excitonic 

transitions was found in the in-plane field geometry. In such a geometry, qualitatively similar 

behavior was reported for pyramidal InGaAs/AlGaAs QDs [2] and interpreted in terms of 

Coulomb correlations. In our case, such an interpretation is supported by analysis of 

diamagnetic coefficients. The lack of significant systematic difference in diamagnetic shift 

allows us to reject an alternative explanation of g-factor variation by increase/decrease of 

barrier penetration by weakly confined hole. 

[1] J. J. Finley et al., Phys. Rev. B 66, 153316 (2002). 

[2] D. Y. Oberli et al., Phys. Rev. B 80, 165312 (2009). 

107 

g-factor of X + , X - , and XX 

3.0 

2.5 

2.0 

1.5 

XX 

X + 

X - 

1.0 

1.0 1.5 2.0 2.5 3.0 

g-factor of X 

Fig. 1. Correlation between Landé factors 

inferred from different excitonic transitions 

in 24 different dots.

TuO6 _______________________________________________________________ 


ControloverCdTeQuantumDotsEmissionusingZnTe-based 

MicropillarCavities 

T.Jakubczyk 1 ,W.Pacuski 1 ,A.Golnik 1 ,C.Kruse 2 ,D.Hommel 2 , 

H.Hilmer 3 ,R.Schmidt-Grund 3 and J.A.Gaj 1 

1 InstituteofExperimentalPhysics,UniversityofWarsaw,ul.Hoża69,00-681Warsaw, 

Poland 

2 InstituteofSolidStatePhysics,UniversityofBremen,Postfach330440,D-28334, 

Bremen,Germany 

3 InstituteforExperimentalPhysicsII,UniversitätLeipzig,Linnéstr.5,D-04103, 

Leipzig,Germany 

Pillarmicrocavitiescontainingquantumdots(QDs)werereportedassystemsenablingcontroloverspatial,energeticandtemporalaspects[1]oflightemission.Intermsof 

applicationsinquantuminformationprocessing[2],coherentcouplingbetweenlightand 

matterobtainedinsuchsystemsisofprimaryimportance.Inthiscontextanextension 

oftheresearchfromtheGaAs-basedsystemstowiderband-gapII-VIbasedonesispromising.Therobustexcitonicstatesandastrongercarrierconfinementinthesematerials 

extendthefunctionalityrangeofsuchQDsystemstohighertemperatures. 

Inthiscommunicationwereportamicrophotoluminescencestudyofpillarcavities 

basedonsuperlattice-baseddistributedBraggreflectors(DBRs)[3],lattice-matchedto 

ZnTe.Micropillarsofdiametersrangingfrom0.7to5µmwereetchedbyfocusedion 

beam(FIB)outofaplanarmicrocavitybasedontheseDBRsandcontainingasingle 

planeofCdTe/ZnTequantumdots. 

BoththeemissionofasingleQDaswellasemissionof 

anensembleofthemwasusedtoexaminedifferentpropertiesofthestructures.WepresentresultsprovingtheabilityofZnTe-basedpillarstoenhancetheQDsemission(see 

Figure).Furthermore,wepresenttheirabilitytoguidethis 

emissionresultinginanenhancedcollectionrate.ThesefeaturesstronglyindicatethepossibilityofconstructingefficientsinglephotonsourcesbasedonCdTeQDs. 

Toinhibittheunwantedemissionintotheleakymodes 

anewapproachwasused.AlateralDBRmadeofyttriastabilizedzirconiaandaluminawassuccessfullydeposited.Wepresentadetailedphotoluminescencestudyoftheobtainedstructures. 

[1]J.M.Gérard,B.Sermage,B.Gayral,B.Legrand,E.Costard,andV.Thierry-Mieg, 

Phys.Rev.Lett.81,1110 

(1998). 

[2]J. P. Reithmaier, G. S ֒ ek, A. Löffler, C. Hofmann, 

S.Kuhn,S.Reitzenstein,L.V.Keldysh,V.D.Kulakovskii,T.L.Reinecke,andA.Forchel,Nature432,197 

(2004). 

[3]W.Pacuski,C.Kruse,S.Figge,andD.Hommel,Applied 

PhysicsLetters94,191108(2009). 

108

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors TuP1 

Exciton and Mn spin dynamics in a nonresonantly coupled pair 

of (Cd,Mn)Te quantum dots 

T. Smoleński 1 , ̷L. Cywiński 2 , M. Goryca, 1 and P. Kossacki 1 

1 Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Ho˙za 

69, 00-681 Warsaw, Poland 


Poland 

It has been shown recently that a spin of a single Mn ion residing inside a quantum 

dot can be optically oriented by circularly polarized light creating spin-polarized excitons 

in the dot [1,2]. In case of experiments in which the absoprtion line corresponding to a 

specific spin state of the Mn was excited resonantly [2], it was argued that the spin relaxation 

of holes (due to phonon scattering and spin-orbit interaction, leading to transitions 

between bright and dark exciton states seen in experiment in Ref. [2]) can explain the 

existence of the Mn optical orientation [3]. 

In experiment from Ref. [1] the spin-polarized excitons were created in the Mn free 

dot which was nonresonantly coupled to an adjacent dot [4] containing a single Mn spin 

[1,5]. The exciton (X) tunnels out of the first dot in a few ps [4], but the timescale on 

which it relaxes to its ground state in the second dot (thereby lowering its energy by 

≈ 0.2 eV) is not precisely know. Depending on whether this relaxation is fast or slow 

compared to the dynamics of the exciton coupled to the Mn spin, different states of the 

X+Mn system are expected to be realized after the relaxation. In order to model both the 

dynamics of the photoluminescence from the second dot, and the Mn spin dynamics (due 

to the sp-d exchange coupling with the exciton), we use the Lindblad generator formalism 

to describe all the relaxation process: the transition from the first dot to the ground 

state of the second dot, the radiative recombination, and the carrier spin relaxation. In 

this way we model both the coherent and the incoherent the processes leading to the 

brightening of dark excitons [5], possible population trapping in the dark state, and Mn 

optical orientation. 

This work was supported by InTechFun (Grant No. POIG.01.03.01-00-159/08), by the 

Homing and the Start programmes of the Foundation for Polish Science supported by the 

EEA Financial Mechanism, and by the Polish Ministry of Science and Higher Education 

as research grants in years 2010-2011. 

[1] M. Goryca, T. Kazimierczuk, M. Nawrocki, A. Golnik, J.A. Gaj, P. Kossacki, P. Wojnar, 

and G. Karczewski, Phys. Rev. Lett. 103, 087401 (2009). 

[2] C. Le Gall, L. Besombes, H. Boukari, R. Kolodka, J. Cibert, and H. Mariette, Phys. 

Rev. Lett. 102, 127402 (2009). 

[3] ̷L. Cywiński, Phys. Rev. B 82, 075321 (2010). 

[4] T. Kazimierczuk, J. Suffczyński, A. Golnik, J.A. Gaj, P. Kossacki, and P. Wojnar, 

Phys. Rev. B 79, 153301 (2009). 

[5] M. Goryca, P. Plochocka,T. Kazimierczuk, P. Wojnar, G. Karczewski, J.A. Gaj, M. Potemski, 

and P. Kossacki Phys. Rev. B 82, 165323 (2010). 

109

TuP2 _______________________________________________________________ 


Three-dimensional anisotropy studies of CdTe quantum dots 

J. Kobak 1 , W. Pacuski 1 , T. Kazimierczuk 1 , J. Suffczy ski 1 , T. Jakubczyk 1 , A. Golnik 1 , 

P. Kossacki 1 , M. Nawrocki 1 , J.A. Gaj 1 , C. Kruse 2 , D. Hommel 2 

1 Institute of Experimental Physics, Faculty of Physics, University of Warsaw, 

ul. Ho a 69, PL-00-681 Warszawa, Poland 

2 Institute of Solid State Physics, University of Bremen, PO.Box 330 440, D-28334 Bremen, 

Germany 

In standard microphotoluminescence study of quantum dots (QDs) optical axis is 

oriented parallel to the growth axis of the sample. Therefore polarization of emitted photons is 

perpendicular to the growth axis of the sample. In this work we present the results of microand 

macro-photoluminescence study of QDs in a configuration with optical axis perpendicular 

to the growth axis. Such measurements were possible since the samples were cleaved and 

their edge was exposed. In our measurements we explore both polarizations parallel and 

perpendicular to the growth axis. 

We studied selforganized CdTe QDs in ZnTe matrix grown by molecular beam 

epitaxy (MBE). Two techniques were used in order to form dots from thin CdTe layer. In the 

first technique the CdTe thin layer was covered by amorphous tellurium at a low temperature. 

Subsequently amorphous tellurium was evaporated at growth temperature before overgrowing 

with ZnTe. In the second technique, the CdTe thin layer was overgrown by ZnTe with high 

Zn content, without changing the temperature. For spectroscopy samples were placed under 

the microscope lens which position was controlled by three xyz piezo translation stages. 

Whole system was immersed in superfluid helium in a magneto-optical cryostat. Lines 

associated to the single QDs we identified with use of single photon correlation 

measurements. 

Two emission bands were observed in the macro-photoluminescence measurements. 

Band seen at lower energy was attributed to quantum dots. This band is strongly polarized in 

direction perpendicular to the growth axis of the sample. Such effect is expected for heavy 

hole excitons. The band located at higher energy was identified as coming from the wetting 

layer. It shows a small degree of linear polarization with a stronger component in direction 

parallel to the growth axis. 

In micro-photoluminescence measurements we have found that more than 99% of 

QDs show the complete polarization perpendicular to the growth axis. This is in agreement 

with macro-photoluminescence results and with prediction done for heavy hole excitons. 

Surprisingly, we have found also sharp emission lines exhibiting a weak polarization degree. 

Moreover, for them the stronger polarization was parallel to the growth axis. Apart from 

polarization properties, such lines exhibit typical properties of QDs: excitation power 

dependence and temporal evolution such as biexciton – exciton cascade observed in photon 

correlation measurements. 

We have done magneto-optical measurements to get a deeper understanding of the 

observed unusual polarization anisotropy. We applied two configurations: with a magnetic 

field in a direction parallel or perpendicular to the growth axis. Results of the polarization 

resolved magnetooptical measurements are discussed in terms of multi-axis anisotropy of 

QDs. 

110

40th _______________________________________________________________ 


Probing electron concentration in epitaxial graphene 

using Raman spectroscopy 

K.Grodecki 1,2 , W.Strupinski 2 , A.Wysmołek 1 , R.Stępniewski 1 , and J.M.Baranowski 2,1 

1 Faculty of Physics, University of Warsaw, Hoża 69, 00-681 Warsaw, Poland 

kacper.grodecki@fuw.edu.pl 

2 Institute of Electronic Materials Technology, Wólczynska 133, 01-919 Warsaw, Poland 

Over the past years, a lot of attention has been attracted to graphene. Its unique 

properties could make it the successor to silicon in electronic applications. Now one of the 

essential problems that must be solved in graphene technology is accurate control of the 

carrier concentration in the structure. Within this communication we would like to let know 

that this problem can be effectively solved by the use of Raman spectroscopy. The Raman 

spectra of graphene-like structures consist of several bands. The most prominent among them 

are so called G and 2D bands. The position of the 2D band is predominantly strain sensitive 

whereas the position of the G band depends both on the intensity and the doping [1, 2]. 

In this communication we show how frequency measurements of G and 2D-band may 

be used to evaluate free carrier concentration in graphene layer. In order to validate this 

method we have examined a set of graphene samples with known electron concentration. 

The measured graphene layers were grown on Si face of 4H-SiC on-axis substrates by 

chemical vapor deposition technique [3]. As determined from the Hall measurements the 

electron concentration of different samples remained between 6x10 12 and 2.4x10 13 cm -2 . 

Micro-Raman measurements were performed at room temperature using single grating 

spectrometer equipped with longpass filters and CCD camera. The size of exciting light spot 

from 532nm Nd:YAG continuous wave laser at the sample surface was approximately 2mm 

in diameter. 

The micro-Raman measurements performed on the samples with different electron 

concentration revealed pronounced shifts of the G and 2D band positions. Basing on the 

strain dependences of these bands from literature data [2] the electron concentration induced 

shift was calculated. This result - 1cm -1 /10 12 cm 2 - remains in compliance with the 

measurements performed within this concentration range for a gated structure freestanding 

graphene measurements [1]. This proves that Raman spectroscopy can be very useful as a fast 

contactless method which allows to determinate the local carrier concentration and strain (up 

to micrometer scale) in graphene structures. 

[1] A. Das, S. Pisana, B.Chakraborty, S. Piscanec, S. K. Saha, U. V. Waghmare, K. S. 

Novoselov, H. R. Krishnamurthy, A. K. Gaim, A. C. Ferrari and A. K. Sood, Nature 

Nanotechnology 3, 210 (2008) 

[2] N. Ferralis, Journal of Materials Science 45, 19, (2011) 

[3] W. Strupinski, K. Grodecki, A. Wysmolek, R. Stepniewski, T. Szkopek, P. E. Gaskell, A. 

Gruneis, D. Haberer, R. Bozek, J. Krupka, and J. M. Baranowski, NANO Letters (2011) DOI: 

10.1021/nl200390e 

111

TuP4 _______________________________________________________________ 


Dynamical control of excitonic fine structure with nanomechanical strain 

M. Zielinski 1 , G. W. Bryant 2 , N. Malkova 2 , J. Sims 3 , W. Jaskolski 1 , J. Aizupura 4 

1 Instytut Fizyki UMK, ul. Grudziądzka 5, 87-100 Toruń, Poland 

2 Atomic Physics Division and Joint Quantum Institute, NIST, 100 Bureau Drive, 

Gaithersburg, Maryland 20899-8423, USA 

3 Information Technology Laboratory, NIST, 100 Bureau Drive, Gaithersburg, Maryland 

20899-8423, USA 

4 Centro Mixto de Fisica de Materiales CSIC-UPV/EHU and Donostia International Physics 

Center, Paseo Manuel Lardizabal 4, Donostia-San Sebastian 20018, Spain 

We show how nanomechanical strain [1,2] can be used to achieve dynamical control 

of electronic and optical properties of semiconductor quantum dots, including exciton fine 

structure of single quantum dots and charge distributions in double quantum dots with 

potential applications in quantum dot based schemes for entangled photon-pair generation and 

manipulating interacting qubits for quantum information processing. 

We use atomistic tight-binding theory [1-4] to describe the response of confined states 

in a self-assembled quantum dot embedded in a nanomechanical cantilever. The internal strain 

due to the lattice mismatch, the external strain and the internal readjustment to minimize the 

applied strain must all be accounted for to model correctly the strain effects [1,2]. We show 

that applied strain can be used to manipulate the fine structure splitting of mechanoexcitons 

by distorting electron and hole charge distributions and rotating hole orientation. Electrons 

and hole levels and charge distributions can shift together or in opposite directions depending 

on how the strain is applied. This gives control for tailoring band gaps and optical response. 

The strain can also be used to transfer electrons and holes between vertically or laterally 

coupled dots, giving a mechanism for manipulating transition strengths and interacting qubits 

for quantum information processing. 

We demonstrate that nanomechanical strain tunes the exchange splittings and rotates 

the polarization of mechanoexcitons, providing energy and phase control of excitons. We 

further demonstrate that nanomechanical strain is a tool to shift electron and hole levels, 

transfer carriers between dots, manipulate mechanoexciton shape, orientation, fine-structure 

splitting and optical transitions rates. 

[1] G.W. Bryant, M. Zielinski, N. Malkova, J. Sims, W. Jaskolski and J. Aizpurua, Phys. Rev. 

Lett. 105, 067404 (2010). 

[2] G.W. Bryant, M. Zielinski, N. Malkova, J. Sims, W. Jaskolski, J. Aizpurua, prepared for 

publication in Phys. Rev. B 

[3] W. Jaskolski, M. Zielinski, G.W. Bryant, J. Aizpurua, Phys. Rev. B 74, 205309 (2006). 

[4] M. Zielinski, M. Korkusinski, and P. Hawrylak, Phys. Rev. B 81, 085301 (2010). 

112

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Non-Markovian noise at the Fermi-edge singularity in quantum 

dots 

Katarzyna Roszak 1 and Tomáˇs Novotný 2 

1 Institute of Physics, Wroc̷law University of Technology, 50-370 Wroc̷law, Poland 

2 Department of Condensed Matter Physics, Faculty of Mathematics and Physics, 

Charles University, 12116 Prague, Czech Republic 

The Fermi-edge singularity is a phenomenon originating from the interaction of conduction 

electrons with localised perturbations and is characterised by a power-law divergence. 

It was first predicted theoretically for X-ray absorption in metals [1] and later 

verified experimentally [2]. The theory then developed [1,3] has been used to describe 

other situations involving a similar Hamiltonian and leading to the same power-law divergence, 

such as resonant tunnelling through localised levels. The proper description of 

the transport set-up is done by an extension of the original Fermi-edge singularity model, 

where no charge transfer between the continuum and the localized level(s) is considered, 

to the interacting resonant level model, which has served recently as an important benchmark 

for novel quantum transport techniques [4]. 

The Fermi-edge singularity in transport through quantum dots occurs in the regime 

where the energy of the quantum dot level(s) is similar to that of one of the leads. The 

change of occupation in the local level(s) during the tunnelling process leads to sudden 

changes in the scattering potential and hence, to truncated singular behaviour of the 

current through the quantum dot at resonance and power-law dependence of the current 

away from resonance [5,6]. As shown in recent experiments [6], noise in this regime 

displays characteristic behaviour (including a super-Poissonian maximum) which cannot 

be accounted for by the Markovian theory. Since the Fermi-edge singularity transport 

setup involves both many-body correlations and quantum coherence it is reasonable to 

expect large non-Markovian corrections in the singularity region. We show that this is 

indeed the case and that including the non-Markovian effects allows us to account for all 

of the qualitative features of the noise. 

[1] G. D. Mahan, Phys. Rev. 163, 612 (1967). 

[2] P. H. Citrin, Phys. Rev. B 8, 5545 (1973). 

[3] G. D. Mahan, Many-Particle Physics (Kluwer, New York, 2000). 

[4] E. Boulat, H. Saleur, and P.Schmitteckert, Phys. Rev. Lett.101, 140601 (2008). 

[5] H. Frahm, C. von Zobeltitz, N. Marie, and R. J. Haug, Phys. Rev. B74,035329 (2006). 

[6] N. Marie, F. Hohls, T. Lüdtke, K.Pierz, R. J. Haug, Phys. Rev. B 75, 233304 (2007). 

113

TuP6 _______________________________________________________________ 


Transport and Spin Properties of CdTe/CdMgTe Quantum Point Contacts 

M. Czapkiewicz, J. Wróbel, V. Kolkovsky, P. Nowicki, M. Aleszkiewicz, M. Wiater and 

T. Wojtowicz 

Instytut Fizyki PAN, Warszawa, Poland 

The spin properties of one-dimensional (1D) semiconductor devices are more strongly influenced 

by electron-electron interactions as compared to two-dimensional (2D) systems. Up to 

now, however, studies of spin characteristics of 1D transport channels are almost exclusively 

devoted to III-V heterostructures and quantum wells [1]. Here we report on fabrication and 

low temperature magnetotransport measurements of quantum point contacts, patterned from ntype 

CdTe/CdMgTe modulation doped quantum well. We expect that the many-body effects are 

quite important in this material since the effective mass is larger and the dielectric constant is 

smaller as compared to GaAs. 

Two-terminal quantum point contacts 

have been made of high quality 2D electron 

gas with concentration n2D= 4.6×10 11 cm −2 

and mobility µ = 0.2×10 6 cm 2 /Vs. The 

nanojunctions of length L≈0.2 µm and lithographic 

width Wlith = 0.45±0.01 µm are 

patterned by e-beam lithography and deepetching 

techniques. The carrier density in the 

device is controlled by means of V-shaped 

side gates which are separated from the constriction 

area by narrow etched grooves, see 

Fig. 1. The differential conductances G have 

been measured in a He-3 cryostat as a function 

of dc source-drain excitation and inplane 

magnetic field by employing a standard 

low-frequency lock-in technique. 

SG 

5 

10 

15 

µm 

etched grooves 

SG 

Figure 1: Atomic force microscopy image 

of quantum point contact formed by chemical 

etching. The width of nano-junction is controlled 

by side gates (SG). 

Data show that G is quantized vs gate voltage, however, conductance steps are reduced 

down to≈ 0.6×(2e 2 /h) and superimposed on reproducible conductance fluctuations (UCF’s). 

We have also found, that the quantization/UCF patterns change considerably when voltages are 

applied asymmetrically to the side gates. Therefore, we argue that transport in studied devices 

is strongly influenced by short range potential fluctuations present in the junction area. However, 

in spite of a disorder, we have been able to observe the Zeeman splitting of 1D transport 

channels at milikelvin temperatures. By comparing obtained splittings with the nonlinear conductance 

data we have been able to determine the effective Landé factor in the constriction. We 

have found that |g ∗ | = 1.7±0.1 in remarkable agreement with bulk value reported for CdTe, 

independently on 1D level index. We conclude that there is no enhancement of electronic g factor. 

This is an unexpected result, since such enhancement, attributed to exchange interaction, 

was always observed for quantum point contacts and quantum wires made of GaAs [2]. 

We acknowledge the support from the Polish Ministry of Science and Higher Education, 

project number N202/103936 and partial support by the European Union within European Regional 

Development Fund (grant Innovative Economy POIG.01.01.02-00-008/08). 

[1] K.-F. Berggren and M. Pepper, Phil. Trans. R. Soc. A 368, 1141 (2010). 

[2] K. J. Thomas et al., Phys.Rev. B 68, 4846 (1998). 

114

40th _______________________________________________________________ 


The Role of Strong Coupling in the Superradiance of Ensembles 

of Quantum Dots. 

Micha̷l Kozub, Pawe̷l Machnikowski 


We present a theoretical description of spontaneous emision from a dense ensemble 

of self-assembled quantum dots (QDs) in the limit of weak excitation. We show that 

the decay rate of the spontaneous emission from the system depends on the number of 

collectively emitting dots, thus confirming the experimental conclusion [1] on the appearance 

of collective (superradiant) emission in the inhomogeneous ensamble of interacting 

dots. However our simulations indicate that interactions over a common electromagnetic 

reservoir are not sufficiently strong to account for the observed increase of the decay rate. 

We therefore introduce additional terms in the interaction potential to make up for the 

discrepancy between the experiment and our simulations. 

In the experiment [1], the decay rate of the luminescence signal was analysed as a 

function of the size of mesas cut out in a planar ensemble of QDs, that is, of the number 

of dots collectively interacting with the electromagnetic field. The observed decay of luminescence 

after a resonant excitation had an approximately exponential character with 

the decay rate increasing as the mesas became larger. This was interpreted as a collective 

effect, due to long range coupling between the dots. 

In this work we model the ensemble of QDs as a system of interacting and collectively 

emitting two-level atoms. In analogy with the experimental procedure, we study the 

emission of systems of dots with randomly selected transition energies that are randomly 

placed (at a fixed density) on squares of different sizes. The evolution of the system 

is simulated using the equations derived in the Power-Zinau-Wooley picture and in the 

Markov approximation, which corresponds to the method of Ref. [2], generalized to nonidentical 

emitters placed in a dielectric medium. We make the additional assumption that 

at most one exciton is present in the system in the initial state, coherently delocalized 

over all the dots (which corresponds to resonant excitation with a very short pulse). We 

calculate the time dependence of the average number of excitons in the dots for system 

parameters corresponding to the experimental situation [1] and show that the population 

decay indeed has an approximately exponential character with rates very close to 

those observed experimentally. This result could not be achieved for dipole-coupled dots, 

without taking into account another type of QD interaction. We show that including a 

short range tunnel coupling between the dots leeds to an increase of the recombination 

rate which is indistinguishable from that obtained for an artificially enhanced long-range 

dipole coupling. In this way we show that the coupling between the quantum dot emitters 

and the electromagnetic vacuum cannot be held fully responisble for the variation of the 

emission rate as proposed in [1]. 

[1] M. Scheibner et al., Nature Physics, 3, 106 (2007). 

[2] R. H. Lehmberg, Phys. Rev. A, 2, 883 (1970). 

115

TuP8 _______________________________________________________________ 


Photoluminescence Linewidth Analysis 

of Single CdMnTe Quantum Dots 

M. Szymura 1;2 , Ł. Kłopotowski 2 , P. Wojnar 2 , K. Fronc 2 , T. Kazimierczuk 3 , 

G. Karczewski 2 and T. Wojtowicz 2 

1 Department of Mathematics and Natural Sciences, 

Cardinal Stefan Wyszyński University, Warsaw, Poland 

2 Institute of Physics, Polish Academy of Sciences, Warsaw, Poland 

3 Faculty of Physics, University of Warsaw, Warsaw, Poland 

Quantum dots (QDs) doped with transition metal ions are interesting from the point of view of 

both basic studies and applications in quantum information processing. Introducing e.g. Mn, 

substantially changes magnetooptical properties of QDs. In particular, the photoluminescence 

(PL) linewidth (γ) for a CdTe QD is about 200 μeV, while for CdMnTe with 20% of 

manganese increases by a factor of 100. In this report, we present a comprehensive study of 

the PL linewidth performed on a large number of dots differing with respect to size and 

manganese concentration. 

Two kinds of structures with CdMnTe QDs were investigated: those with ZnTe barrier and 

with ZnMnTe barrier. All quantum dots were grown by molecular beam epitaxy (MBE) on 

GaAs substrate. A 4 μm thick buffer CdTe layer was first deposited. Next a ZnTe (and 

ZnMnTe) barrier layer was grown. QDs were developed from 6 monolayers of CdMnTe. PL 

measurements were performed as a function of the magnetic field up to 5T at a temperature of 

2K. We study samples with manganese concentration between 1% to 20%. 

The presence of manganese ions caused giant Zeeman splitting of electronic states of QDs.We 

- 

analyzed two circular polarizations. In practice, the transitions in polarization quickly 

disappear as a result of efficient spin relaxation between the Zeeman split subbands. We 

reproduce the transition energies with a Brillouin function, which allows us to evaluate 

manganese concentration and temperature. 

Broadening of the PL transitions from Mn-containig QDs is due to magnetization fluctuations. 

Therefore, γ depends on magnetic field, QD volume and manganese concentration and 

temperature [1]. At the absence of magnetic field, for a QD with 1.5% manganese we find γ 

≈4.5 meV. As the magnetic field is increased, γ decreases by about a factor of 2 in 5T. This 

decrease manifests the freezing of the magnetic fluctuations in increased magnetic field. We 

reproduce this narrowing of the linewidth with magnetic field with a formula derived from 

fluctuation dissipation theorem [1]. We obtain a good agreement between the results of 

calculations and experiment. Moreover, the above analysis allows us to evaluate the QD 

volume. We find that QDs emitting in higher energies have smaller volume, as expected. 

[1] G. Bacher et al. Phys. Rev. Lett. 89, 127201 (2002). 

116

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Statistical Study of the Inter-Dot Excitation Transfer in CdTe/ZnTe 

Quantum Dots. 

Maciej Koperski 1 , Tomasz Kazimierczuk 1 , Mateusz Goryca 1 , Andrzej Golnik 1 , 

Jan A. Gaj 1 , Michał Nawrocki 1 , Piotr Wojnar 2 and Piotr Kossacki 1 


Hoża 69, 00-681 Warsaw, Poland 

2 Polish Academy of Sciences, Lotników 32/46, 02-668 Warsaw, Poland 

Photoluminescence (PL) experiments are the most basic tool for characterization of 

semiconductor quantum dots (QDs). They provide broad range of information on the 

excitonic complexes, such as neutral excitons (X), trions (X + , X - ) and biexcitons (XX), 

confined in a zero-dimensional system. Measurements of PL spectra as a function of 

excitation laser energy is known as photoluminescence excitation technique (PLE). Features 

in PLE spectra are usually related to excited exciton states or phonon-replica. Additionally, in 

the system of self organized CdTe/ZnTe quantum dots, very sharp resonances at high energy 

are often observed. They were attributed to the efficient excitation transfer between 

neighboring dots [1]. Diverse experiments have been reported, taking advantage of the 

excitation transfer, such as polarization conversion [1] and orientation of the magnetic ion in 

dots with single manganese atom [2]. Despite extensive studies, the detailed mechanism of the 

inter-dot tunneling remains not entirely clear. 

Here we present the results of detailed statistical analysis of the energy distribution of 

resonances detected in PLE spectra. We studied MBE grown samples containing single layer 

of self organized CdTe/ZnTe quantum dots. The samples were placed in a microphotoluminescence 

setup at low temperature (1.5 - 15 K). The PL was excited using a tunable 

dye laser in the range 570−610 nm. During measurements we have selected more than 200 

single quantum dots for which exciton complexes (X, X+, X- and XX) were identified, and 

for which the sharp resonances related to inter-dot transfer were observed. Each resonance 

correspond to the absorption with creation of neutral exciton, after which the exciton is 

transferred to the second dot and subsequently recombines. The difference between energies 

of neutral excitons in the two dots varied in our experiments between 80 meV and 300 meV 

and was mainly limited by the experimental setup. This distance is larger than typical distance 

between s-shell and p-shell groups of lines which yields about 50meV in our case. We 

analyzed the occurrence probability versus the energy distance between neutral exciton line in 

the emitting dot and the exciton energy in the absorbing dot (resonance energy). 

This analysis revealed relatively flat distribution of the resonances, which shows that 

levels participating in the tunneling are not collected in separate groups (p-shell, d-shell etc.). 

This might be interpreted as a result of smearing discrete distribution into continues one due 

to the statistical scatter between different dots or significant broadening of the excited states 

in each emitting dot. In any case, the observed flat distribution suggest that the density of 

states participating in the tunneling is flat or the tunneling occurrence is not limited by the 

presence of excited states in the emitting dot. 

[1] T. Kazimierczuk, J. Suffczyński, A. Golnik, J. A. Gaj, P. Kossacki and P. Wojnar, Phys. 

Rev. B 79, 153301 (2009). 

[2] M. Goryca, T. Kazimierczuk, M. Nawrocki, A. Golnik, J. A. Gaj, P. Kossacki, P. Wojnar 

and G. Karczewski, Phys. Rev. Lett. 103, 087401 (2009) 

117

TuP10 _______________________________________________________________ 


Phonon influence on the weak measurement of double quantum 

dot spin states. 

̷L. Marcinowski 1 , M. Krzy˙zosiak 1,2 , K. Roszak 1 , P. Machnikowski 1 , 

R. Buczko 3 , and J. Mostowski 3 


2 Beijing University of Technology, 100124 Beijing, China 


The occupation of a double quantum dot (DQD) can be measured by coupling one of the 

dots to a quantum point contact (QPC) and monitoring the current flowing through the 

QPC [1]. This originates form the interaction between the quantum dot and QPC electrons 

which shifts the energy level in the QPC depending on the dot state influencing the 

tunneling rate through the point contact. A single tunneling event is a weak measurement 

of the dot and provides a small amount of information about the system state. A series 

of tunneling events constitutes a continous measurement process in which the descrete 

current yields a growing amount of information on the system state, but also gradually 

destroys quantum coherence and localizes the state, consistently with the von Neumann 

projection principle. 

The same measurement scheme can be used to distinguish two-electron spin-singlet 

and spin-triplet states in DQDs [2]. This is based on Pauli exclusion: when the spin-triplet 

state requires the electrons to be localized in different dots (only QD ground states are 

taken into account), double dot occupation is allowed for the spin-singlet state. Hence, 

monitoring the fluctuations in the QPC current allows one to perform a measurement in 

the singlet-triplet basis. 

In this work we study the effect of phonon-induced transitions which are present in this 

solid state system [3] on the QPC current and the measurement-influenced evolution of the 

DQD state. In the strong bias regime, when the measurement is possible in the absence 

of phonons [2], phonon-induced relaxation leads to a reduction of the double occupation, 

and hence, to quenching of the current response. In the weak bias case the energy transfer 

from the tunneling electron is insufficient to excite the QD to a doubly occupied state 

and the phonon reservoir serves as a source of noise which makes the excitation possible; 

this is reflected in the current trace. 

[1] T. M. Stace and S. D. Barrett, Phys. Rev. Lett. 92, 136802 (2004). 

[2] S. D. Barrett and T. M. Stace, Phys. Rev. B 73, 075324 (2006). 

[3] K. Roszak and P. Machnikowski, Phys. Rev. B 80, 195315 (2009). 

118

40th _______________________________________________________________ 


InfluenceofCarrierTrappingontheOpticalPropertiesof 

InAs/InPQuantumDashes 

P.Kaczmarkiewicz,A.Musiał,G.Sęk,P.Podemski,J.Misiewicz, 

P.Machnikowski 

InstituteofPhysics,WrocławUniversityofTechnology,50-370Wrocław,Poland 

WemodeltheopticalpropertiesofhighlyanisotropicInAs/InPquantumdots,also 

referredtoasquantumdashes(QDashes)[1]. Thosestructuresarecharacterizedbya 

non-uniformshapeandpresenceofwidthfluctuations[2]whichcanprovideadditional 

confinementinthesystem. Trappingofcarriersinthepotentialfluctuationsleadsto 

quantitativeandqualitativechangeintheopticalpropertiesofthesystem.Theexciton 

groundstateexhibitsQD-like(stronglyconfined[3])propertieswhichcanexplainthe 

temperaturedependenceofthedegreeoflinearpolarizationofemittedradiation. 

WeshowhowthetransitionratesdependonQDashshapeparameters(amplitude 

andpositionofthewidening)andcalculateemissionspectraforsingleQDashesandfor 

ensemblesofQDashes. Wealsostudythepolarizationpropertiesofradiationemitted 

bythesystem. WeconfirmthataQDashwidthfluctuationleadstostrongtrapping 

ofcarriers,whichresultsinloweringtheanisotropyofanexcitongroundstateinspite 

ofstrongelongationofthewholestructure. Suchacharacteroftheconfiningpotential 

manifestsitselfintheexperimentalresultsbyaloweredvalueofthedegreeoflinear 

polarizationatlowtemperaturesandlowexcitationconditions. 

TheinvestigationoftheopticalpropertiesofQDashesisimportantfromthepointof 

viewofpossibleapplications.IthasbeenshownthatQDashesmayhaveseveraladvantagesoverothernanostructures,especiallyinlaserapplicationsfortelecommunication[1]. 

Understandingofthepolarizationpropertiesandthereforecarrierconfinementregimeis 

alsoimportantforconstructingpolarization-insensitiveopticalamplifiers[4]. 

Webaseourmodelingoftheelectron-holesystemontheeffectivemassmethodwith 

light-heavyholebandmixingtakenintoaccount[5].Theholestatesareassumedtoconsist 

mostlyofaheavy-holecomponentwithsmalladmixtureoflight-holestates.Thislightholeadmixturedependsontheanisotropyoftheholewavefunctionviathemomentum 

dependenceoftherelevantelementofthe k·pHamiltonian. Interferencebetweenthe 

radiationemittedbythelight-andheavy-holecomponentsleadstotheappearanceof 

apreferredpolarizationaxis,paralleltothestructureelongation. Thepresenceofan 

additionalconfinementduetotheshapefluctuationdecreasestheanisotropyofanexciton 

groundstateandreducestheDOP.Inourmodelingweconsiderthecaseofasingle 

excitonconfinedinaQDash,whichcorrespondstoexperimentalmeasurementsinthe 

weakexcitationregime. Coulombcorrelationsareincludedwithintheconfigurationinteractionscheme. 

[1]J.P.Reithmaier,G.Eisenstein,A.Forchel,Proc.IEEE95,1779(2007). 

[2]H.Deryetal.,J.Appl.Phys.95,6103(2004). 

[3]G.Sęketal.,J.Appl.Phys.105,086104(2009). 

[4]P.Podemskietal.,Appl.Phys.Lett.93,171910(2008). 

[5]P.Kaczmarkiewiczetal.,ActaPhys.Pol.A(inprint). 

119

TuP12 _______________________________________________________________ 


CdSe/ZnS Colloidal Quantum Dots with Alloyed Core/Shell Interfaces: 

a Photoluminescence Dynamics Study 

Konrad Dziatkowski 1,2 , Daniel Ratchford 1 , Thomas Hartsfield 1 , Xiaoqin Li 1 , 

Yan Gao 3 and Zhiyong Tang 3 

1 Department of Physics, University of Texas at Austin, Austin TX 78712, USA 

2 Institute of Experimental Physics – University of Warsaw, 00-681 Warsaw, Poland 

3 National Center for Nanoscience and Technology, 100190 Beijing, P. R. China 

The colloidal semiconducting nanocrystals – and quantum dots (QDs) in particular – 

have been a subject to extensive studies driven by their promising photonic or photovoltaic 

applications. There are numerous features of colloidal QDs, to mention only long term 

photostability, that make them superior to other single emitters, e.g dye molecules. 

Nevertheless, their optical properties are not yet optimal from the viewpoint of technological 

utilization. One of the main unresolved issues with respect to colloidal QDs is fluctuations 

of photoluminescence (PL), or so called “blinking”. Despite intense experimental 

and theoretical research effort, the detailed microscopic mechanism of PL intermittency 

remains obscure, and so far no single theoretical model accounts for all observations [1]. 

The most comprehensive explanation postulates that when a QD is charged, a non-radiative 

Auger ionization suppresses PL and makes the emitter appearing dark [2]. Recently, 

the diminishing of Auger process and, in consequence, quenching of blinking was observed 

in selenium-based ternary QDs, even though these QDs possessed extra charge [3]. 

Subsequent theoretical study claimed this observation to be a general feature of the emitters 

with smoothed quantum confinement potential, since under such conditions the transition 

matrix element for the Auger recombination is greatly reduced [4]. 

This paper reports a comprehensive study of PL dynamics in chemically-synthesized 

CdSe/ZnS QDs with alloyed core/shell interfaces. Due to the softening of the structural 

interface between the core and the shell such emitters manifest a quantum yield of up 

to 80 % [5]. The employed technique of time-correlated single photon counting enabled 

measurements of the decay of exciton luminescence from both the ensemble and individual 

QDs. For decreasing emission wavelength, the ensemble data revealed systematic increase 

of total decay rates with greater variation, as it is expected that smaller emitters are more 

influenced by the surface/interface trap states. In experiments performed on single QDs, 

the PL trajectories exhibited familiar two-state blinking pattern, despite alloying between 

CdSe and ZnS. We suggest that in core/shell QDs with a large band gap offset, as in case 

of CdSe/ZnS system, the compositionally graded energy profile at the interface may not 

be smooth enough to suppress non-radiative Auger recombination and prevent blinking. 

[1] P. Frantsuzov, M. Kuno, B. Janko, and R. A. Marcus, Nature Physics 4, 519 (2008). 

[2] A. L. Efros and M. Rosen, Physical Review Letters 78, 1110 (1997). 

[3] X. Wang, X. Ren, K. Kahen, M. A. Hahn, M. Rajeswaran, S. Maccagnano-Zacher, 

J. Silcox, G. E. Cragg, A. L. Efros, and T. D. Krauss, Nature 459, 686 (2009). 

[4] G. E. Cragg and A. L. Efros, Nano Letters 10, 313 (2010). 

[5] W. K. Bae, K. Char, H. Hur, and S. Lee, Chemistry of Materials 20, 531 (2008). 

120

40th _______________________________________________________________ 


Spectroscopy of Indirect Excitons in Vertically Stacked CdTe 

Quantum Dot Structures 

K. Kukliński, ̷L. K̷lopotowski, K. Fronc, P. Wojnar, T. Wojciechowski, 

M. Czapkiewicz, J. Kossut, G. Karczewski, and T. Wojtowicz 

Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 

02–668 Warsaw, Poland 

We show that by means of an electric field we can tune the energy levels in vertical 

single quantum dot (QD) pairs and study transitions related to recombination of indirect 

excitons. 

Embedding QDs in vertical field effect structures enables electrical control of the QDs 

charge state and allows to study properties related to Coulomb interactions. There are 

many reports on studies of direct excitons in single CdTe/ZnTe QDs. However, for this 

material system, no data is reported on indirect excitons, i.e. excitons related to recombination 

of an electron and a hole localized in two separate QDs. Obtaining a controlled 

coupling between two QDs is interesting from the point of view of basic research and for 

realization of a quantum gate, the building block of a quantum computer. 

In this communication, we present the results of spectroscopic studies of indirect excitons 

in vertically stacked QD structures. The QDs were embedded in the insulating 

region of a p–i–Schottky diode grown by molecular beam epitaxy on a GaAs substrate. 

The layer sequence was the following: a 4-µm thick p–doped ZnTe buffer, a 100 nm of 

undoped ZnTe, two QD layers separated by a 4 or 8 nm ZnTe spacer, a 50 nm thick 

ZnTe cap and a 50 nm ZnMgTe blocking barrier. QDs were formed from a 2D CdTe layer 

six monolayers thick. Ohmic contacts were established to the p–type ZnTe and a Al/Au 

Schottky contacts were deposited on top of the sample. Single QD pairs were accessed 

through 200 nm diameter shadow mask apertures. The photoluminescence (PL) signal 

was excited with a 532 nm laser beam focused to a 2 µm spot with a microscope objective. 

PL spectra were measured at 10 K as a function of a bias voltage. 

At zero bias we observe PL transitions from single pairs of QDs. We identify charge 

states from uncoupled dots. As the bias is increased, transitions shift due to the quantum 

confined Stark effect. Evidence of the presence of indirect excitons in the measured PL 

spectra are transitions strongly shifting in the electric field, as a consequence of greater 

value of dipole moment compared with direct excitons. We observe two types of lines: 

these for which Stark shift is about 0.5–1 meV/V and these with 4–7 meV/V. In accordance 

with the above conclusion, we identify the first transitions as related to direct 

excitons, and the latter as indirect. We assume that the dipole moment of the indirect excitons 

is pind = ed, where d is the spacer layer thickness. Therefore, the Stark shift of the 

indirect exciton allows us to calibrate the electric field in our structure. We find that this 

field is a factor of four smaller than expected from a capacitor formula: F = (U−Ubi)/W, 

where U and Ubi is the applied and built–in voltage, respectively, and W is the width of 

the intrinsic region. Having calibrated F, we find that the dipole moment for the direct 

exciton pdir ∼ 1 nm, thus pind ≈ 4(8)pdir. With decreasing reverse bias we observe both 

the red– and blue–shifted indirect exciton transitions. We assume that due to strain– 

enhanced nucleation, the QDs in the top layer are larger than the bottom dots. Basing 

on the band profiles of our structures, we conclude that the blue–shifted transitions are 

related to the recombination of the electron and hole localized in the top and the bottom 

dot, respectively. In turn, red–shifted indirect excitons are associated with the recombination 

of the electron and hole in the bottom and the top dot, respectively. 

121

TuP14 _______________________________________________________________ 


Collective spontaneous emission from pairs of quantum dots: 

the role of coupling and system geometry 

Wildan Abdussalam, Anna Sitek, Pawe̷l Machnikowski 

Institute of Physics, Wroc̷law University of Technology, 50-370 Wroc̷law, Poland 

We study the role of various types of coupling between semiconductor quantum dots 

(QDs) in the collective spontaneous emission of double dot systems. Excitons delocalized 

in closely spaced QDs recombine in a different way than in a single QD due to collective 

interaction of the two emitters with the quantum radiation field [1]. While for noninteracting 

dots this collective effect appears only for almost identical dots (with the 

transition energies within the emission line width), coupling between the dots leads to 

accelerated or slowed down emission even for dots with different transitions energies, 

which is manifested in the linear and non-linear response from these systems [2]. 

In this contribution, we study the spontaneous emission from an exciton confined in 

a double quantum dot. We focus on the similarities and differences between the cases of 

radiative (long-range, dipole) and tunnel coupling between the excitons in the dots. We 

show that for strictly identical dots the oscillating nature of the dipole coupling on long 

distances leads to non-monotonic dependence of the radiative decay rate on the inter-dot 

separation, which is not present in the case of tunnel coupling. However, for a double 

dot system with a realistic, technologically feasible mismatch of transition energies, the 

collective effects disappear completely well before these oscillations become relevant. In 

this case, there is no qualitative difference between the two physically different coupling 

types and the system dynamics in the two cases becomes indistinguishable for appropriate 

values of the coupling parameters. 

We believe that these findings may shed some light on the interpretation of the experiment 

[3] in which enhanced emission was observed in a quantum dot ensemble in which 

the dipole coupling energies on the typical inter-dot distances were much smaller than the 

average transition energy mismatch between the dots. 

[1] A. Sitek, P. Machnikowski, Phys. Rev. B 75, 035328 (2007). 

[2] A. Sitek, P. Machnikowski, Phys. Rev. B 80, 115319 (2009); 80, 115301 (2009). 

[3] M. Scheibner, T. Schmidt, L. Worschech, A. Forchel, G. Bacher, T. Passow, D. Hommel, 

Nature Physics 3, 106 (2007). 

122

40th _______________________________________________________________ 


Tunneling Transfer Protocol in a Quantum Dots Chain Immune 

to Inhomogeneity 

Kamil Korzekwa and Pawe̷l Machnikowski 


We propose a quantum dot (QD) implementation of a quantum state transfer channel. 

The proposed channel consists of N vertically stacked QDs with the nearest neighbour 

tunnel coupling, placed in an axial electric field. The QD chain isdoped with oneelectron. 

The terminal QDs are assumed to provide a stronger binding for the electron. In this 

way, the states with electron on the terminal dots are energetically separated from other, 

but remain indirectly coupled via the QD chain. The inhomogeneity of the QD chain 

is included by using normal distribution for the values of tunnel couplings and electron 

energy levels. By applying an external electric field along the chain, the terminal QDs 

are brought to resonance, which leads to an efficient occupation transfer. 

Our proposal requires a global electric field as the only control means, therefore it 

satisfies the requirement of simplicity. We study the conditions of getting the quantum 

state transfer and compare the results with the previously proposed protocol [1]. We show 

that in our model the transfer fidelity for a homogenous QD chain is independent of the 

chains length. We show also that controlling the global electric field is enough to make 

the system resistant to inhomogeneity of both QD energies and tunnel coupling. Within 

our model we use the real QD parameters and show that almost perfect tunneling transfer 

is possible. 

Sinceourprotocolfulfillsthesimplicityrequirementitisexperimentallyfeasible. Since 

thetransferisindependentoftheQDinhomogeneityitcouldbeusedtotransferexcitation 

in a real QD chain. 

a) 

|P| 2 

1 

0.75 

0.5 

0.25 

0 

0 25 50 75 100 

t [ns] 

b) 

|P| 2 

1 

0.75 

0.5 

0.25 

0 

0 25 50 75 100 

Evolution of the occupation of on the initial QD (solid line), the final QD (dashed line) and the 

QDs inside the chain (dotted line) of 10 QDs spin chain. Electron energies in the QD’s normally 

distributed with standard deviation ∆ = 10meV and tunnel couplings J = 10meV. Terminal 

QDs energy E = 50meV a) No external electric field; b) Terminal QDs tuned to resonance by 

an external field. 

[1] A. Wójcik, T. ̷Luczak, P. Kurzyński, A. Grudka, T. Gdala, and M. Bednarska, Phys. 

Rev. A 72, 034303 

123 

t [ns]

TuP16 _______________________________________________________________ 


Thermal Quenching of Photoluminescence from epitaxial InGaAs/GaAs 

Quantum Dots with High Lateral Aspect Ratio 

Anna Musiał 1 , Grzegorz S k 1 , Aleksander Mary ski 1 , Paweł Podemski 1 , 

Janusz Andrzejewski 1 and Jan Misiewicz 1 

Andreas Löffler 2 , Sven Höfling 2 , Stephan Reitzenstein 2 , Johann Peter Reithmaier 2,* 

and Alfred Forchel 2 

1 Institute of Physics, Wrocław University of Technology, Wrocław, Poland 

2 Technische Physik, Universität Würzburg, Wilhelm Conrad Röntgen-Center for Complex 

Material Systems, Am Hubland, D-97074 Würzburg, Germany 

Self-assembled In0.3Ga0.7As quantum dots (QDs) [1] have already been demonstrated as 

good candidates for testing QED phenomena due to enhanced exciton oscillator strength [2] 

being a result of increased structure volume and weaker carrier confinement [3]. 

This report concerns temperature dependence of photoluminescence (PL) in both 

ensemble and single QD regime. At 5K, PL spectra consist of two bands related to the wetting 

layer (WL) and QD ensemble, separated by rather small energy (~ 35 meV) indicated shallow 

confining potentials for holes and electrons. At low temperatures WL emission dominates and 

there is a rather insignificant carrier transfer to the dots because most of the WL states are 

localized [3]. At higher temperatures (> 30K) carriers are released becoming extended into the 

WL plane and carrier redistribution increases the QD emission with respect to the WL one. 

Thermal quenching of PL from QD ensemble reveals activation energy of about 30 meV 

corresponding well with the confinement energy identifying a primary carrier loss mechanism 

– release of carriers to WL. This has also been confirmed at the single QD level. The 

activation energy varies between 15-30 meV reflecting the dot size and hence carrier 

confinement distribution. In case of single QD the impact of WL is stronger, because the 

probability that a carrier returns to the same dot and emits is lower than the probability of 

carrier to get back to any of the dots contributing to the ensemble PL. In a very few cases a 

fingerprint of 2 nd significantly smaller activation energy is observed, suggesting that carrier 

localization inside those structures is not present or localization energy is very low (below 1 

meV - the resolution of the method) meaning that at low temperatures excitons are always 

extended over the entire QD and experience large coherence volume. This was further 

supported by polarization-resolved temperature dependent PL to probe the symmetry of 

confining potential by obtaining the degree of linear polarization. It is low at 5K (~6%) and 

decreases slightly with temperature due to emission from higher energy states reflecting lower 

effective anisotropy [4]. This can be understood as a result of very weak confining potential 

for electrons in agreement with 8 band kp calculations giving DOP values below 10%. 

[1] A. Löffler, J. P. Reithmaier, A. Forchel, A. Sauerwald, D. Peskes, T. Kümmell and G. 

Bacher, J. Cryst. Growth 286, 6 (2006). 

[2] J. P. Reithmaier, G. S k, A. Löffler, C. Hofmann, S. Kuhn, S. Reitzenstein, L. Keldysh, 

V. Kulakovskii, T. Reinecke and A. Forchel, Nature 432, 197 (2004). 

[3] G. S k, A. Musiał, P. Podemski, M. Syperek, J. Misiewicz, A. Löffler, S. Heling, L. 

Worschech and A. Forchel, J. Appl. Phys. 107, 96106 (2010). 

[4] P. Kaczmarkiewiecz, A. Musiał, G. S k, P. Podemski, P. Machnikowski and J. Misiewicz, 

Acta Phys. Pol. A (2011), in press. 

* Currently at: Institute of Nanostructure Technologies and Analytics, Technische Physik, Universität Kassel 

124

40th _______________________________________________________________ 


Excitonic Magnetoabsorption of Cylindrical Quantum Disks 

P. Schillak and G. Czajkowski 

Department of Theoretical Physics, University of Technology and Life Sciences 

Al. Prof. S. Kaliskiego 7, 85-789 Bydgoszcz, Poland 

Potential applications of semiconducting nanostructures in novel optoelectronic devices 

gain the interest in the optical properties of quantum disks, quantum wires and the 

other low-dimensional objects. Here we investigate the influence of excitonic effects on 

the optical properties of quantum disks in the external magnetic field. We propose the 

theoretical approach which enables to calculate the optical functions for low-dimensional 

structureswithcylindricalsymmetryexposedtotheexternalmagneticfielddirectedalong 

the symmetry axis. We consider an interacting electron-hole pair inside the semiconducting 

nanostructure with hard-wall potential of finite height (different for an electron and 

a hole) at the boundaries. The different anisotropic effective masses are taken inside and 

outside the structure. The novelty of our approach is that the six-dimensional eigenvalue 

problem is transformed into the equivalent eigenvalue problem given by the system of the 

coupled two-dimensional second order differential equations. Differential equations are 

solved numerically. As an example, we present in Fig. 1 the magnetic field dependent 

excitonic energy spectrum for the InP disk with the radius R = 8 nm and the height 

d = 4 nm. Additionally, numerical results are compared with experimental data taken 

from the paper by Dewitz et al. [1]. Having the energies and wave functions, we apply 

the real density matrix approach [2,3] 

which gives the optical functions including 

magnetoabsorption and the 

magnetic field dependent dielectric 

tensor for light- and heavy-hole excitons. 

In this approach the linear 

response is described by the set of 

coupledequationsfortwo-pointcorrelation 

function Y(re,rh) and the 

Maxwellianfieldequation. TheconstitutiveequationforY(re,rh)hasa 

form of Schrödinger’s equation with 

a source term, which reflects the 

light-matter interaction. Numerical 

computations were performed 

for In0.55Al0.45As/Al0.35Ga0.65 and 

CdSe quantum disks. Our numerical 

results are in a good agreement 

with experimental data. 

relative energy [meV] 

120 

100 

80 

60 

40 

20 

0 

0 20 40 60 

magnetic field B [T] 

Figure 1: The calculated (full lines) and measured 

(circles) relative positions of energy levels 

as functions of the applied magnetic field. 

[1] C. v. Dewitz, F. Hatami, M. Millot, J. M. Broto, J. Léotin, and W. T. Masselink, 

Appl. Phys. Letters 95, 151105 (2009). 

[2] G. Czajkowski, F. Bassani, and L. Silvestri, Rivista del Nuovo Cimento, 26(5-6), pp. 

1-150 (2003). 

[3] P. Schillak and G. Czajkowski, phys. stat. sol. (c), 5 2495 (2008). 

125

TuP18 _______________________________________________________________ 


Spontaneous emission from double quantum dots: collective 

effects and carrier-phonon kinetics 

Pawe̷l Karwat, Anna Sitek, Pawe̷l Machnikowski 


We study theoretically the evolution of luminescence from a double quantum dot in the 

presence of carrier-phonon interaction. We show that the spontaneous emission from 

this system is determined by the interplay of collective effects, which are due to the 

interaction between the two emitters and their common radiative reservoir, and phononinduced 

transitions (typically on a much shorter time scale). 

The time-resolved luminescence from double quantum dots is an interesting subject of 

study as it yields information on the carrier kinetics under the joint action of two reservoirs: 

electromagnetic vacuum to which the exciton ultimately decays in the spontaneous 

emission (radiative recombination) process and the lattice excitations which may dephase 

the charge states and lead to transitions between the confined states. One of the experiments 

[1] revealed surprising temperature dependence of the luminescence life time which 

first grows as the temperature is increased and then decreases. This enhancement of the 

exciton lifetime with increasing temperature is in striking contrast to the single dot case 

where the life time drops down with temperature, which can easily be associated with 

various possible thermally activated non-radiative channels. 

In this presentation, we model the system kinetics using a Markovian Lindblad generator 

for the spontaneous emission process [2] and a non-Markovian time-convolutionless 

dissipator that accounts for the phonon-related kinetics [3]. We show that the quasiequilibrium 

distribution of the occupations of the two lowest energy eigenstates sets up 

within several picoseconds after the excitation. Since one of these states is more active 

optically (“brighter”) this leads to temperature dependence of the emission rate and to 

non-monotonic dependence of the luminescence life time similar to that observed in the 

experiment. 

[1] C. Bardot, M. Schwab, M. Bayer, S. Fafard, Z. Wasilewski, P. Hawrylak, Phys. Rev. 

B 72, 035314 (2005). 

[2] A. Sitek, P. Machnikowski, Phys. Rev. B 80, 115319 (2009). 

[3] P. Machnikowski, K. Roszak, A. Sitek, Acta Phys. Pol. A 116, 818 (2009). 

126

40th _______________________________________________________________ 


Cathodoluminescence studies of the II – VI semiconducting quantum dots 

grown by molecular beam epitaxy 

P. Łach 1 , A. Reszka 1 , G. Karczewski 1 , P. Wojnar 1 , T. Wojtowicz 1 , A. Kamińska 1 , 

and A. Suchocki 1,2 

1 

- Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668, Warsaw, 

Poland 

2 

- Institute of Physics, Kazimierz Wielki University, Weyssenhoffa 11, Bydgoszcz 85-072, 

Poland 

Self-assembled quantum dots (QDs) as zero-dimensional structures are very 

intensively studied optically and electrically on account of their shape and small sizes. Our 

QDs consisted of II-VI compounds were grown on (100)-oriented GaAs substrate by Stranski- 

Krastanov mode by molecular beam epitaxy method (MBE). The obtained objects have 

diameter and height of the order of 10 - 40 nm and 1 - 14 nm, respectively. The QDs were 

embedded in a ZnTe matrix with thickness of about 1.5 µm and they were composited of 6 

monolayers. A whole was covered by a thin cap (100 nm). The concentration of the QDs was 

equal to 10 9 – 10 10 of QDs per 1 cm 2 . 

We have measured the cathodoluminescence (CL) spectra of such structures as a 

function of the temperature. The luminescence was excited by electron beam with 

accelerating voltage of the order of 5 – 15 kV. This experiment was carried out for CdTe, 

CdMnTe and CdSe QDs. We have checked behaviour of the CL signals in different places on 

these samples. This dependence shows certain non-uniform distribution of QDs in the 

examined samples. With increase of the temperature the spectra became considerably wider 

and their intensities decreased. It results from excitons redistribution between QDs (the 

carriers were intercepted from a wetting layer to a bigger QD which emits a light in lower 

energies). The possible mechanisms of the temperature luminescence quenching are nonradiative 

exciton recombination due to the Auger effect and disappearance of the quantum 

confinement at higher temperatures. We discuss the both mechanisms in this paper. 

The examples of the results of the photoluminescence (PL) and cathodoluminescence (CL) 

measurements (on the left) and the temperature dependences for CdTe QDs (on the right) are 

presented below for comparison. 

CL intensity [au] 

PL intensity [au] 

40000 

30000 

20000 

10000 

0 

20K 

2,00 2,05 2,10 2,15 2,20 2,25 2,30 

50000 

40000 

30000 

20000 

10000 

0 

Energy [eV] 

70K 

60K 

50K 

40K 

30K 

1,95 2,00 2,05 2,10 2,15 2,20 2,25 2,30 2,35 

Energy [eV] 

T=60K 

T=57K 

T=53K 

T=48K 

T=43K 

T=34K 

T=28K 

T=20K 

T=11K 

CL intensity [au] 

14000 

12000 

10000 

8000 

6000 

4000 

2000 

10 20 30 40 50 60 70 

Temperature [K] 

10 20 30 40 50 60 

In this case we have measured the PL and CL spectra to about 100K. The CdMnTe and CdSe 

QDs have given the CL signals even over 200K. 

Acknowledgement: This work was partially supported by the grant of the Polish Ministry of 

Science and Higher Education for years 2007-2011. 

127 

PL intensity [au] 

14000 

12000 

10000 

8000 

6000 

4000 

2000 

Temperature [K]

TuP20 _______________________________________________________________ 


Raman spectroscopy of CdTe/ZnTe quantum dots 

E. Zielony 1 , E. Popko 1 , Z. Gumienny 1 , P. Kamyczek 1 , A. Henrykowski 1 , J. Jacak 1 , 

G.Karczewski 2 

1 Institute of Physics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 

50-370 Wroclaw, Poland 

2 Institute of Physics, Institute of Physics Polish Academy of Science, al. Lotnikow 32/46, 


Semiconducting low-dimensional structures of CdTe quantum dots embedded in ZnTe matrix 

have been investigated by micro-Raman spectroscopy. A reference ZnTe sample (without 

dots) was also studied for comparison. Both samples were grown by molecular beam epitaxy 

technique on the p-type GaAs substrate. The QD sample consists of 3µm thick p + -type 

ZnTe:N buffer deposited on the p-type GaAs substrate, 1µm undoped ZnTe, a layer of CdTe 

quantum dots and 0.3µm of undoped ZnTe cap. The CdTe self assembled quantum dots were 

grown in the atomic layer epitaxy (ALE) growth mode by deposition of six monolayers of 

CdTe. The process of QD formation was induced by covering the CdTe layers with an 

amorphous tellurium layer and its subsequent thermal desorption [1]. The presence of 

quantum dot structure was confirmed by photoluminescence measurements. The Raman 

measurements have been performed at room temperature with the help of the T64000 Jobin 

Ivon spectrometer configured in the triple subtractive mode of operation. The samples were 

excited by an Ar 2+ laser working at a wavelength of 514.5 nm. The Raman spectra have been 

recorded for different acquisition parameters of the measurement. For the reference and QD 

sample localized longitudinal (LO) phonons of 210cm -1 wavenumber associated with the 

ZnTe layer [2] are observed. In the case of QD sample another broad band corresponding to 

the LO CdTe phonon related to the QD-layer appears at a wavenumber of 160 cm -1 [2]. Such 

behavior does not exhibit the Raman spectra for the reference sample. For both samples 

additionally tellurium - related peaks at wavenumbers around 120 cm -1 and 140 cm -1 are 

detected. It has been noticed that the intensity of CdTe and ZnTe LO phonon peaks decreases 

with increasing time of a laser beam exposition while the signal associated with Te - like 

Raman peaks increases. The latter is caused by the laser damage in the ZnTe layer followed 

by the formation of Te aggregates on the ZnTe surface. The Raman measurements confirm 

the presence of CdTe layer of quantum dots in the investigated material. 

[1] P. Wojnar, J. Suffczynski, K. Kowalik, A. Golnik, M. Aleszkiewicz, G. Karczewski, and 

J. Kossut, Nanotechnology 19, 235403 (2008). 

[2] V. S. Vinogradov, et al., Physics of the Solid State, Vol. 50, No. 1, 2008. 

128

40th _______________________________________________________________ 


Quantum interference in charge transport via the quantum dots 

coupled between the metallic and superconducting leads 

J. Barański and T. Domański 

Institute of Physics, M. Curie Sk̷lodowska University, 20-031 Lublin, Poland 

We analyze the effects of quantum interference observable in the Andreev current 

induced through the double quantum dots coupled between an isotropic superconductor 

and metallic leads. Superconducting properties are transfered on such nanostructures 

due to the proximity effect and they have qualitative influence on the nonequillibrium 

phenomena, especially in a regime of the subgap bias voltage |V | ≤ ∆/|e|. We will 

discuss condictions necesarry for observing the Fano resonances and shall try to account 

for their interplay with the strong correlation effects. 

129

TuP22 _______________________________________________________________ 


Bound Magnetic Polaron Molecule in Diluted Magnetic 

Semiconductors within the Heitler-London Approximation 

Henryk Bednarski 1 and Jozef Spa̷lek 2 

1 Centre of Polymer and Carbon Materials, Polish Academy of Sciences, 34 M. 


2 Marian Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 

30-059 Kraków, Poland 

Recently developed by us a complete microscopic theory of the bound magnetic polaron 

molecule (BMPM) in diluted magnetic semiconductors [1] is reformulated in a reduced 

spin-state space. Namely, we solve the BMPM problem by taking into account the 

Heitler-London form of the two-electron wave function in the four dimensional spin-state 

space (comprising one singlet and three triplet states) and include the thermodynamic 

fluctuations of the magnetization due to the localized 3d spins in the Gaussian form. 

In this manner, the role of covalency effects can be clearly identified and its influence 

analysed in detail. Moreover, within this formulation the quantum aspect of the BMPM 

problem is also accounted for, as it results from quantum-mechanical indistinguishability 

of the two impurity electrons and is contained in the antisymmetric nature of their 

two-electron wave function. Therefore, the formulation of the BMPM theory provides us 

with the opportunity of studying the physical origin of the competition between ferroand 

antiferro-magnetic interactions of the impurity pair of electrons in diluted magnetic 

semiconductors. 

[1] H. Bednarski, J. Spa̷lek, arXiv:0912.0662v4, submitted to Phys. Rev. B. 

130

40th _______________________________________________________________ 


Intersubband polaritons in strongly pumped microcavities 

M. Zału ny and A. Kozłowski 

Institute of Physics, M. Curie-Skłodowska University, Pl. M. Curie-Skłodowskiej 1, 20-031 

Lublin, Poland 

It is well known that resonant microstructures have an important role in the 

enhancement of nonlinear optical processes in multiple quantum well (MQWs) structures. So 

far most research has concentrated on the nonlinear effects connected with excitonic coupling 

to the microcavity (MC) mode [1]. In our recent paper [2] we have discussed theoretically the 

nonlinear intersubband response of the MQWs embedded in MCs. The simplest case, when 

strong probe wave acts alone, has been considered. It has been shown, that in the strongcoupling-regime 

the saturation effect leads to the evolution of the absorption spectra from a 

pair of simple harmonic oscillators to highly anharmonic ones. 

The experimental and theoretical results reported in [1] indicate that in MCs the pumpprobe 

nonlinear excitonic effects [leading to the formation of the so-called Mollow absorption 

spectrum (MAS) [3]] are much more easily observed due to the enhancement of the optical 

field by the MC. Stimulated by this fact in this paper we discuss theoretically the problem of 

the formation of the intersubband MAS in the MQW-MC systems. 

Like in our previous paper, we employ a semiclassical approach based on the transfer 

matrix formalism (TMF) and the so-called sheet model [2,4] (The sheet, modeling the optical 

response of the QW, is characterized by the 2D conductivity.) For simplicity we neglect the 

influence of the electron-electron interaction on the nonlinear intersubband response. It has a 

good justification when the surface electron concentration in QW is relatively small (�10¹¹ 

cm²) and the wavelength of incident radiation is not too large ( �10 m) [5]. To achieve a 

sufficiently strong coupling between intersubband excitation and incident radiation the 

experimentally studied systems usually contain a large number of QWs. Practically, the QWs 

occupy almost the whole space between mirrors. Unfortunately, in such type of systems, 

contrary to those studied in [1], the strength of the optical field acting on each QW is 

different. The numerical simulations reported in this paper are performed taking into account 

also the above mentioned effect. 

The calculations of the angle resolved (probe) absorption spectra are decomposed into 

two sequential stages. First, the pump wave propagation in the system is described neglecting 

the energy transfer between the (strong) pump and (weak) probe waves. The spatial pump 

field distribution in the MC-MQW system is calculated taking into account the saturation 

effect. The case when the response to pump beam has bistable character [2] is also considered. 

At second stage, the linear problem of the probe beam propagation in the system is solved 

taking into account fact the that the Mollow 2D (intersubband) conductivity of each QW [3,6] 

depends on the pump field intensity, at the position of the QW, determined in the first stage. 

For better understanding of the role of the spatial variation of the pump field in the MC we 

also present a simplified approach based on a Fabry-Perot model and the “mean field” 

approximation [2]. 

[1] B. Beveaurd, et al. CR Acad. Sci. IV-Phys., 2, 1439 (2001) and references therein. 

[2] M. Zału ny and C. Nalewajko, J. Appl. Phys. 107, 123106 (2010). 

[3] B. R. Mollow, Phys. Rev. 188,1969 (1969); Phys. Rev. A 5, 227 (1972). 

[4] M. Zału ny and C. Nalewajko, J. Appl. Phys. 99, 026104 (2006. 

[5] R. A. Kaindl, et al., Phys. Rev. B 62, 161308(R) (2001). 

[6] P. Meystre and M. Sargent III, Elements of quantum optics (Springer, Berlin, 1990). 

131

TuP24 _______________________________________________________________ 


Magneto-Optical Studies of Narrow Band-Gap Heterostructures with Type 

II Quantum Dots InSb in an InAs Matrix 

Mikhail S. Mukhin 1 , Yakov V. Terent’ev 1 , Leonid E. Golub 1 , Mikhail O.Nestoklon 1 , 

Boris Ya. Meltser 1 , Alexey N. Semenov 1 , Victor A. Solov’ev 1 , Alla A. Sitnikova 1 , Alexey A. 

Toropov 1 and Sergey V. Ivanov 1 

1 Ioffe Physical-Technical Institute of Russian Academy of Sciences, 26 Polytekhnicheskaya, 

St Petersburg 194021, Russian Federation 

Spin is the only electron internal degree of freedom, and utilizing it in the new 

generation of semiconductor devices is the main goal of semiconductor spintronics. Today 

spintronics focuses mainly on diluted magnetic semiconductors (DMS) where ferromagnetism 

and giant Zeeman splitting can be obtained due to exchange interaction between free carriers 

and Mn ions. Most of the work has been focused on II-VI DMS such as CdMnTe or ZnMnSe 

and some others. Enhanced magnetic properties of these materials exist only at cryogenic 

temperatures due to paramagnetic behavior of the magnetic ions. A lot of recent investigations 

have been focused on doping III-V semiconductors into a DMS state. Although III-V DMS 

demonstrate higher Curie temperature, Mn is much less soluble here than in II-VI 

semiconductors [1]. Another issue is that in III-V compounds magnetic doping harmfully 

affects emission properties and, moreover, changes conductivity to p-type. We have proposed 

a new approach to the problem based on using narrow band-gap III-V compounds possessing 

the largest intrinsic electronic g-factor, which are InSb and InAs [2]. 

Present research is focused on spin-related phenomena in low-dimensional InSb/InAs 

heterostructures and continues our preliminary studies [3]. Magneto-optical investigations of 

type-II InSb QDs in an InAs matrix and their theoretical consideration are reported. In(Sb,As) 

heterostructures incorporating monolayer-scale InSb insertions in the InAs matrix, possessing 

high recombination efficiency, were fabricated by MBE. Circularly polarized 

photoluminescence has been measured in the 

polarization, % 

100 

80 

60 

40 

20 

0 

-20 

T=2K 

B=4T 

0,1 1 10 

Excitation Intensity, W/cm 2 

Faraday geometry, allowing direct probing of the 

electron spin state. Experiments were carried out in 

the temperature range from 2 to 140 K and 

excitation density 0.1 – 20 W/cm 2 . It was found that 

the polarization degree varies form 100% -minus 

up to 15% -plus, depending on the excitation 

intensity and temperature. The physical model of the 

phenomenon is developed, based on the selection 

rules for optical transitions involving heavy holes, 

dependence of the oscillator strength on the excitation density, inherent for indirect in space 

optical transitions that only are allowed here, and an analysis of equilibrium population of 

energy levels. The detailed calculation of the energy spectrum of charge carries, performed 

within a tight-binding approximation, is also presented. The results of the theoretical 

treatment are in good agreement with experimental data. The simulation of the experimental 

data revealed that the oscillator strength of the optical transitions of electrons with the spin 

oriented either along or against the magnetic field vector differs by approximately 1,8 times. 

[1] T.T. Chen, C.H. Chen, W.S. Su et al., J. Appl. Phys. 93, 9655 (2002). 

[2] Ya.V. Terent’ev, A.A. Toropov, B.Y. Meltser et al., Semiconductors 44, 194 (2010). 

[3]Ya.V. Terent’ev, O.G. Lyublinskaya, A.A. Toropov et al., Semiconductors 43, 635 (2009). 

132

40th _______________________________________________________________ 


Phonon-assisted tunneling between hole states in double 

quantum dots 

Krzysztof Gawarecki, Pawe̷l Machnikowski 


In this work, we present a theoretical analysis of hole states in double quantum dots 

(DQDs). The system under consideration, consist two, coupled, vertically stacked dots 

with one trapped hole. We study hole states in a realistic model which takes into account 

the system geometry and strain in the DQD. In present work, we also investigate 

phonon-related processes in such a system. We derive phonon-assisted relaxation between 

two lowest hole states and compare those results with the previous one for electrons [1,2]. 

The relaxation rates are calculated as a function of external axial electric field. Carrierphonon 

couplings via both deformation potential and piezoelectric interactions can be 

predominant for different parameters. As shown previously [3] the ground state in such 

molecule can be antibonding [3], which corresponds to recent experiments[4]. In consequence, 

for some distance between dots (relevant to ground state bonding–antibonding 

transition) relaxation rate can be very small. 

DQDs, can be used for designing quantum-coherent devices, including spin-based 

quantum bits. Information can be encoded on carrier states in such structures. However, 

phonon-related processes are inevitable in a cristal environment and may limit the 

feasibility of implementing quantum control in these systems. In consequence, it is essential 

to understand not only the spectral properties of various kinds of semiconductor 

nanostructures but also the relevant phonon-induced processes. 

Our model [1] is based on a k·p approximation for a single particle in a strained selfassembled 

structure. The local band structure in a such a system is obtained from the 

8-band Hamiltonian with strain-induced terms (Bir-Pikus Hamiltonian).We solve the 4x4 

part (light- and heavy holes with two possible spin orientation) of this hamiltonian. Interation 

with the conduction band, was included via quasi-degenerate perturbation theory. 

Next, we calculate the the valence band edges and the effective mass for heavy and light 

holes as a function of the spatial position. The hole wave functions are calculated within 

a multi-component envelope function approximation combined with a Ritz variational 

method. Finally, the Fermi golden rule is used to obtain the relaxation rates between the 

lowest energy eigenstates. 

[1] K. Gawarecki, M. Pochwa̷la, A. Grodecka-Grad and P. Machnikowski, 

Phys. Rev. B 81, 245312 (2010). 

[2] K. Gawarecki, P. Machnikowski, Acta Phys. Pol. A (in press), arxiv:1007.1577 (2010). 

[3] J.I. Climente et al., Phys. Rev. B 78, 115323 (2008). 

[4] M.F. Doty et al., Phys. Rev. Lett. 102, 047401 (2009). 

133

TuP26 _______________________________________________________________ 


Intermediate band formation for electrons and holes in an 

inhomogeneous chain of quantum dots 

Igor Bragar, Krzysztof Gawarecki, Pawe̷l Machnikowski 


We study the electron and hole states of a chain of non-identical, vertically stacked quantum 

dots (QDs). It has been proposed [1] that inserting such a structure in the intrinsic 

region of a p-i-n junction solar cell could increase the photocurrent due to sequential 

absorption of low energy (below-bandgap) photons. While this idea has been gaining 

growing experimental support in the recent years [2], it still seems unclear whether the 

underlying physics corresponds to the intermediate band concept [3] as the band formation 

in a quantum dot chain may be strongly suppressed by the energy inhomogeneity. 

In this presentation we use a simple model of a tunnel-coupled chain of dots containing 

one electron or one hole. By using the energy and coupling parameters obtained from 

realistic k.p calculations [4], we are able to relate the spectral properties of the chain as 

well as the localization properties of the carrier wave functions to the actual geometry of 

the system (dot sizes and inter-dot separations). We study how the pseudo-band formed 

of the ground states confined in the QDs disintegrates upon increasing the inhomogeneity 

of the electron and hole energies. We discuss the impact of localization on the interband 

absorption from the pseudo-band to extended (bulk) states, which is a prerequisite for the 

functionality of the photovoltaic device. We formulate the conditions for the strength of 

the coupling (hence the dot separation) as compared to the degree of the inhomogeneity 

that must be satisfied in order for the system to support delocalized states. 

[1] V. Aroutiounian, S. Petrosyan, A. Khachatryan, K. Touryan, J. Appl. Phys. 89, 2268 

(2001). 

[2] Y. Okada, T. Morioka, K. Yoshida, R. Oshima, Y. Shoji, T. Inoue, T. Kita, J. Appl. 

Phys. 109, 024301 (2011). 

[3] A. Luque and A. Martí, Phys. Rev. Lett. 78, 5014 (1997). 

[4] K. Gawarecki, M. Pochwa̷la, A. Grodecka-Grad, P. Machnikowski, Phys. Rev. B 81, 

245312 (2010). 

134

40th _______________________________________________________________ 


Modelling of 1D-2D structural transitions in small Yukawa 

clusters 

Olga Rancova, Egidijus Anisimovas 

Department of Theoretical Physics, Vilnius University, Saul˙etekio al. 9, LT-10222 

Vilnius, Lithuania 

We study structural transitions that take place in the simplest finite-size systems and 

are analogous to phase transitions in the macroscopic limit [1]. The model system consists 

of a small number of identical interacting charged particles in an anisotropic trap, where 

the particles form stable ordered structures known as Wigner crystals [2]. These are 

observed in diverse systems as electrons on liquid He, ions in traps, 2D semiconductor 

quantum dots, dusty plasmas, macroscopic model systems [3]. Recent developments of 

experimental techniques allowed direct investigation of structural and dynamic properties 

of systems consisting of just a few or several tens of particles under different external 

conditions that can be modelled numerically. 

In present research we model 1D-2D dimensional structural transition caused by decreasing 

anisotropy of the confining potential that is one of the simplest cases of continuous 

phase transitions. Such dimensional transitions called ”zigzag transitions” are studied 

experimentally and modelled numerically [4, 5]. 

The model system consists of N identical charged particles interacting through pairwiseYukawapotentialVin 

= r −1 exp(−κr)withscreeningparameterκandconfinedby2D 

asymmetric parabolic potential Vc = x 2 +α 2 y 2 . The potential interaction energy strongly 

dominates over the kinetic energy. Thus, we are concerned with the minimization of the 

total potential energy. α > 1 squeezes the confining potential inducing structural transitionsofthesystem. 

ThenumericaltechniquecombiningtheMetropolisprocedureandthe 

Newtonoptimizationmethodisusedtoobtaintheenergeticallyfavourableconfigurations. 

The calculations are performed for different κ changing the value of α. 

In present research we investigate the simplest systems up to N = 9 undergoing 

1D-2D structural transition. Changing the potential parameter α gradually we explore 

dependence of the order parameter of the system 〈y〉, defined as average system width 

in the anisotropy dimension, on the potential anisotropy parameter looking for evidences 

of the phase transition. When α reaches a critical value αc the system order parameter 

drops to zero and we obtain a power-law behaviour of the order parameter 〈y〉 ∝ (αc−α) γ 

in the vicinity of this critical point (γ is a critical exponent). We find that in this area 

γ ≈ 0.5 in all cases investigated. Whereas [5] suggests γ = 0.387 in N = 5,κ = 3 case. 

We obtain that the value of the critical exponent changes when the potential anisotropy 

parameter value departs from the critical point. 

Acknowledgments O. Rancova is funded by Lithuanian Science Council (grant No. 

SF-PD-2009-08-17-0054). 

[1] O. Rancova, E. Anisimovas, and T. Varanavičius, Phys. Rev. E 83, 036409 (2011). 

[2] E. Wigner, Phys. Rev. 46, 1002 (1934); C. C. Grimes and G. Adams, Phys. Rev. 

Lett. 42, 795 (1979); E. Y.Andrei, G. Deville, D. C. Glattli, F. I. B. Williams, E.Paris, 

and B. Etienne, Phys. Rev. Lett. 60, 2765 (1988). 

[3] A. V. Filinov et.al., Phys. Rev. Lett. 86, 3851 (2001); M. Saint Jean et.al., Europhys. 

Lett. 55, 45 (2001); D. Block et.al., Phys. Plasmas 15, 040701 (2008). 

[4] A. Melzer, Phys. Rev. E 73, 056404 (2006). 

[5] T. E. Sheridan and K. D. Wells, Phys. Rev. E 81, 016404 (2010). 

135

TuP28 _______________________________________________________________ 


EfficientCoulombmixingbetweensingle-and 

biexcitonstatesinInAsnanocrystals 

P.Kowalski,P.Machnikowski 

InstituteofPhysics,WrocławUniversityofTechnology,50-370Wrocław,Poland 

Multipleexcitongeneration(impactionization)innanocrystalsisaprocess,inwhich 

absorptionofasinglephotonleadstogenerationofmultipleelectron-holepairs. This 

effecthasbeenobservedexperimentally[1,2]andmayincreasetheefficiencyofsolarcells. 

Whileearlierpapersreportedquantumefficienciesreaching700%[3],laterreportssuggestthatthosefigureswereoverestimatedandtheactualyielddoesnotexceed170%[4]. 

Thiscontroversymightberesolvediftheprocessisbetterunderstoodtheoretically. 

Inourpreviouswork[5]wehaveshownthatcoherenttwo-pairgenerationwithasingle 

absorbedphotonispossibleduetoCoulombindirectmixingofsingle-exciton(onepair) 

andbiexciton(two-pair)configurations.However,forlowenergystatesthisprocessisin 

generalveryinefficientsincethetypicalmagnitudeoftheCoulombmatrixelement(tens 

ofmeV)ismuchsmallerthantheaverageseparationbetweentheenergylevels(hundreds 

ofmeV). 

Forhighenergystatesthespectrumoftwo-pairconfigurationsismuchmoredense.In 

thatrangetypicalseparationofstatescoupledtoasinglepairisontheorderof100meV 

(forthenanocrystalradiusof7nm).Thestrengthofthecouplingstillreaches100meV. 

Hence,weexpectstrongmixingbetweenthe1-pairand2-pairconfigurationswhichcan 

leadtoamoreefficientbiexcitongeneration. 

[1]R.D.Schaller,V.I.Klimov,Phys.Rev.Lett.92,186601(2004). 

[2]R.D.Schaller,J.M.Pietryga,V.I.Klimov,NanoLett.7,3469(2007). 

[3]R.D.Schaller,M.Sykora,J.M.Pietryga,V.I.Klimov,NanoLett.6,424(2006). 

[4]M.TuanhTrinhet.al.,NanoLett.8,1713(2008). 

[5]P.Kowalski,P.Machnikowski,ActaPhys.Pol.114,1187(2008). 

136

40th _______________________________________________________________ 


Strongly disordered wetting layer in the InAs/GaAs self-assembled 

quantum dots system 

K. Gołasa 1 , M. Molas 1 , J. Borysiuk 1 , Z. R. Wasilewski 2 and A. Babiński 1 

1 Faculty of Physics, University of Warsaw, Hoża 69, 00-681 Warszawa, Poland 

2 Institute for Microstructural Sciences, National Research Council, Ottawa, Canada 

A wetting layer (WL) is an inevitable result of the formation of quantum dots (QDs) in 

the Stranski–Krastanow growth mode. It is usually assumed that the WL is a thin, highly 

strained quantum well, on which three-dimensional islands grow. However, in real systems 

the morphology of the WL can be more complex. In particular substantial indium fluctuations 

in the WL, which give rise to confinement of carriers have recently been identified [1]. 

In this communication we address the question of growth conditions necessary to form 

such strongly disordered WL. We investigate two samples A and B grown with different 

parameters using molecular beam epitaxy. While growing both samples, a substrate rotation 

was stopped during the InAs layer deposition in order to obtain a gradient of InAs coverage 

across the wafer. The amount of deposited InAs was chosen in such a way as to have a 

continuous variation of the dot density, starting with just InAs WL to fairly high density of 

InAs QDs on each wafer. In the reference sample A, grown in usual conditions, such the 

procedure resulted in an expected evolution of the low-temperature photoluminescence across 

the wafer. Low InAs coverage resulted in the WL-related emission centred at 1.44 eV, which 

disappeared from the spectrum with increasing intensity of the QDs emission due to 

increasing density of QDs grown. In the 

sample B the scenario was different. The 

lowest InAs coverage resulted in QDs 

emission but no emission from the WL (see 

lowest spectrum in Fig. 1). At the expected 

energy range of the WL-emission several 

sharp lines due to recombination of confined 

single excitons and biexcitons were 

observed. At higher InAs coverage a weak 

emission related to a thin WL (denoted with 

an arrow in Fig. 1) was observed, which 

disappeared at even higher InAs coverage 

leaving just the QDs emission in the 

1,25 1,30 1,35 1,40 1,45 

spectrum. The observed behaviour suggests that the WL does not form a continuous twodimensional 

layer before the onset of the QDs formation in the sample B. Instead, twodimensional 

platelets form, which can confine electrons and holes. With higher InAs coverage 

the platelets merge giving rise to usually observed WL. Our conclusions are supported with 

results of transmission electron microscopic study of the samples morphology. 

We present details of the growth procedure and discus their effect on the morphology 

of the investigated samples. We also discuss possible applications of self-assembled QDs 

grown with no continuous WL. 

[1] A. Babiński, J. Borysiuk, S. Kret, M. Czyż, A. Golnik, S. Raymond and Z. R. Wasilewski, 

Appl. Phys. Lett. 92, 171104 (2008). 

137 

PL intensity [arb.u.] 

Energy [eV] 

WL 

Fig.1. The μ-PL spectra from three positions of 

the investigated sample. 

InAs nominal coverage

TuP30 _______________________________________________________________ 


Optical transformation of zero-dimensional confinement in the 

CdTe/CdMgTe multiple quantum wells 

M. Molas 1,* , K. Gołasa 1 , J. Łusakowski 1 , T.Wojtowicz 2 , and A. Babi ski 1 

1 Faculty of Physics, University of Warsaw, Ho a 69, 00-681 Warszawa, Poland 

2 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warszawa, Poland 

Zero-dimensional confinement in semiconductor structures, which is crucial for many optoelectronic 

applications, may result from several factors influencing potential energy of carriers. Most intensely 

investigated are quantum dots (QDs) formed in Stranski-Krastanov growth mode [1,2] or due to composition 

fluctuations in thin quantum wells (QWs) [3]. There are, however, systems in which the confinement results 

from a more complicated potential energy pattern [4,5]. In this communication we report on QDs which in our 

opinion fall to the latter category as they can be transformed by optical illumination. 

An active part of the investigated structure consisted of 20 CdTe QWs, each of a 16 nm width, 

separated by a 48 nm-wide Cd0.8Mg0.2Te barriers. Both the QWs and the barriers were uniformly doped with 2 × 

10 16 cm -3 iodine atoms acting as donors. Broad optical emission band related to the QWs was observed around 

1.6 eV. Moreover, a few discrete emission lines were observed at a lower energy. A more detailed analysis of 

these lines, based on excitation power dependence of their intensity and polarization-sensitive measurements of 

their optical anisotropy, allowed for their attribution to 0D-confined neutral excitons and biexcitons. 

A characteristic feature of the observed single-dot spectra was their instability against a high excitation powerdensity. 

Series of spectra in excited with a relatively low (I = 0.1 W) excitation power-density separated by 2 

min exposure to a high power light (I = 350 W) are shown in Fig. 1. It can be appreciated that the spectra 

change as a result of a high intensity illumination (see Fig.1 a - c) and a new lineshape, stable against subsequent 

high-density illumination was obtained (see Fig. 1 c - d). 

An analysis of the observed metastable behaviour of the spectra led us to conclusion that the 

confinement of carriers, responsible for the spectra, results partially from intrinsic electric fields due to ionized 

Luminescence (a.u.) 

d) 

c) 

b) 

a) 

1.535 1.540 1.545 1.550 

Energy (eV) 

1.555 1.560 1.565 

Figure 1. The -PL spectra from one position of the 

investigated sample 

donors and partially due to local potential 

fluctuations inherent to the QW growth process. 

Existence of such mixed QDs (MQDs) have 

previously been proposed on the basis of farinfrared 

spectroscopic measurements of the 

investigated structure [4, 5]. A large (from 20 

eV to nearly 120 eV) dispersion of the optical 

anisotropy of excitons confined in the MQDs 

suggests a substantial asymmetry of the 

respective lateral potential. The observed 

transform-ation of MQDs is proposed to be 

related to ionization of donors which changes 

the potential fluctuations pattern. A longer 

exposure to a high intensity light leads to 

formation of a different potential fluctuations 

pattern which is reflected by a different 

luminescence lineshape. Discussion of obtained 

results in terms of potential fluctuations in doped QW is presented. 

Partial financial support by Polish Ministry of Higher Education contract N N515071937 

is acknowledged. 

[1] M. Bayer, et al, Phys. Rev. B 65, 195315 (2002). 

[2] G. Karczewski, et al, Appl. Phys. Lett. 74, 3011 (1999). 

[3] L. Besombes, et al, phys. stat. sol. (a) 178, 197 (2000). 

[4] K. Karpierz, et al, Acta Phys. Polonica A 112, 237 (2007). 

[5] K. Nogajewski, et al, Acta Phys. Pol. A 114, 1259 (2008). 

* corresponding author : maciej.molas@fuw.edu.pl 

138

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OpticalPropertiesofInGaAsQuantumDotson(100)GaAs 

SubstratesFormedbyDropletEpitaxy 

MichałKozub 1 ,AnnaMusiał 1 ,GrzegorzSęk 1 ,JanMisiewicz 1 , 

VerenaZürbig 2 andJohannPeterReithmaier 2 

1 InstituteofPhysics,WrocławUniversityofTechnology,50-370Wrocław,Poland 

2 InstituteofNanostructureTechnologiesandAnalytics,TechnischePhysik,Universität 

Kassel,Heinrich-Plett-Str.40,34132Kassel,Germany 

Thepresenceofawettinglayer(WL)inalasingsemiconductormicrostructureintroducesanaditionalandunwantedchannelforcarrierlossandnonradiativerelaxation, 

significantlyreducingtheefficiencyofthedevice. However,inacommonIII-Vsystem 

grownbyself-assemblytheexistenceofthewettinglayerisanintrinsicpropertyofthe 

growthmodeandisunlikelytobeavoided.BecauseoftheWLsdeterioratinginfluence, 

techniquesofgrowthoflowdimensionalstructuresaimingtoreducetheWLorevento 

allowthegrowthofnanostructureswithouttheWLatallarebeingsought. 

Weattemptasystematicstudyoftheinfluenceoftemperatureandflowrateonthe 

formationofawettinglayerinanInGaAs/GaAsquantumdot(QD)systemgrownby 

the’dropletepitaxy’method[1,2],andfurtherhowthegrowthconditionchangesaffect 

theopticalpropertiesoftheentirestructure.SeveralQDsamplesgrownattemperatures 

between 410and 500 o Candgrowthratesof80-110nm/hhavebeeninvestigatedby 

photoluminescence(PL)andcontactlesselectroreflectance(CER).Incaseofthelatter, 

duetoenhancedsensitivityofthemodulationtechniqueitwaspossibletofollownot 

onlytheQDs,butalsotheWLsopticaltransitionsalongthevariatinggrowthcondition 

parameters.Ourfindingssuggestthatwithdecreasingthesubstratetemperature,surface 

diffusioncanbeefficientlyreducedthusenablingustohindertheassemblyofthewetting 

layer. TheWL-relatedopticaltransitionsarewellresolvedathighertemperatures(i.e. 

500 o C),furtherfollowedbyacorrespondingCERsignalintensitydropandbroadening, 

tofinallydisappearfortemperaturesaslowas 410 o C.Weassumethatthedecrementof 

growthtemperature(and/orgrowthrate)renderstheWLdiscontinuousandcausesitto 

coverasmallfractionofthesurfaceonlyforthelowesttemperatures(growthrates). 

AsboththechangesinthegrowthconditionsanddisappearanceoftheWLareexpectedtoaffecttheopticalpropertiesofquantumdots,theQDopticaltransitionshave 

alsobeeninvestigatedvsthetechnologicalparameters. Firstofall,thecombinationof 

PLandCERallowedustodeterminethetransitionenergiesrelatedtoQDs.Then,we 

derivetherespectiveactivationenergiesfromPLthermalquenchingmeasurementsina 

temperaturerangefrom5to300Kinordertodetectareductionofthermally-induced 

losseswithdiminishingWL.Eventually,thechangesinthesurfacedensityofthedots 

havebeenstudiedbymeansofPLwiththespatialresolutionofabout1micrometer, 

whichallowedthedisclosureofthesubstructureofemissionpeaksfromtheensemble 

relatedtosinglequantumdotemissionlinesoreventhesplitofspectraintosharplines 

relatedtosingledots. 

[1]N.Koguchi,S.Takahashi,T.Chikyow,J.CrystalGrowth111,688(1991). 

[2]V.Zrbig,A.Gushterov,L.Lingys,M.Benyoucef,J.P.Reithmaier,Int.MBEConf., 

Berlin,Germany(August,2010). 

139

TuP32 _______________________________________________________________ 


Magnetooptical study of excitons confined in potential fluctuations in 

the CdTe/CdMgTe quantum well 

M. Molas 1,* , K. Gołasa 1 , T. Kazimierczuk 1 , J.Łusakowski 1 , T.Wojtowicz 2 , 

and A. Babi ski 1 

1 Faculty of Physics, University of Warsaw, ul. Ho a 69, 00-681 Warszawa, Poland 

2 Institute of Physics, PAS, Al. Lotników 32/46, 02-668 Warszawa, Poland 

The low dimensional systems based on quantum dots (QDs) are intensely investigated 

for their applications in efficient light sources and detectors tuned in a wide range of 

wavelengths from near infrared to ultraviolet. A three-dimensional confinement of excitons 

can be achieved in self-assembled QDs [1], on fluctuations at interfaces of thin quantum 

wells (QWs) or in disordered thin QWs [2, 3]. However, it was recently shown that also in 

wider single or multiple doped QWs local potential fluctuations can also lead to the QD-like 

confinement [4, 5]. 

We report on magneto-optical properties of sharp excitonic photoluminescence (PL) 

lines related potential fluctuations, which are observed from a sample with a single QW of a 

modulated thickness. An active part of the sample consisted of a 30.1 nm wide CdTe QW, 

sandwiched between two Cd0.8Mg0.2Te barriers. A 5 nm wide iodine doping layer was added 

in the Cd0.8Mg0.2Te barrier. Results of low-temperature micro-PL measurements, performed 

in magnetic field are presented. 

Optical emission from the QW was observed in energy range between 1.81 eV to 

1.83 eV, which reflected the change in the QW thickness. At lower energy, at several 

positions on the sample a few discrete emission lines were observed. The effect of sample 

temperature, magnetic field, and detection polarisation was studied. Neutral biexcitons and 

excitons confined to a single fluctuation-related QD were identified. We found that the 

optical anisotropy of observed excitonic features ranged from about 10 eV to nearly 

160 eV, which suggests a broad distribution of lateral potential asymmetry. Energy 

dispersion of neutral exciton states amounts to 22 meV, which suggests a substantial 

distribution of the confining potential. The values of effective excitonic Lande factor of 

excitons ranged from |g*| = 1.8 to 2. 

We propose to explain our observations in a model of potential fluctuations in the QW 

resulting from a strongly disordered layer of iodine-doping. In regions of the highest iodine 

surface density the effect of electrostatic potential on the QW is the strongest. Confined 

electronic and hole states in the QW in such regions are strongly affected by the Quantum 

Confined Stark Effect (QCSE), which leads to a local decrease of the QW band-gap. In areas 

with a lower iodine density the effect is weaker and the QW bandgap is only weakly affected. 

Fluctuations of the effective QW bandgap due to the QCSE resulting from fluctuations of 

remote ionized iodine donor density are responsible in our opinion for observed QD-like 

confinement of electrons and holes in the investigated structure. 

[1] For review, see D. Bimberg et al, Quantum Dot Heterostructures (Wiley, New York, 1999). 

[2] L. Besombes, et al, Phys. Stat. Sol. (a) 178, 197 (2000). 

[3] D. Gammon, et al, Phys. Rev. Lett. 76, 3005 (1996). 

[4] K. Karpierz, et al, Acta Phys. Pol. A 112, 237 (2007). 

[5] K. Nogajewski, et al, Acta Phys. Pol. A 114, 1259 (2008). 

* corresponding author : maciej.molas@fuw.edu.pl 

140

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Mixed Correlation Phases In Elongated Quantum Dots 

A. Ballester 1 , J. M. Escartín 2 , J. L. Movilla 1 , M. Pi 2 , and J. Planelles 1 

1 Departament de Química Física I Analítica, Universitat Jaume I, Box 224, E-12080, 

Castelló, Spain 

2 Departament ECM, Facultat de Física, IN2UB, Universitat de Barcelona, E-08028, 

Barcelona, Spain 

Nanorods (NRs) are an elongated variant of quantum dots (QDs) with a highly 

anisotropic confining potential. These nanostructures constitute the bridge between zerodimensional 

QDs and one-dimensional quantum wires (QWs). Nanodumbbells (NDs) are 

another type of elongated structures. These structures are NRs sandwiched between two 

spherical caps, typically of a different material. The theoretical study of colloidal 

semiconductor NRs and NDs is of particular interest because of the ability to synthesize these 

kinds of nanostructures with precise size and shape control [1,2]. 

The unusual long length of the NRs leads to characteristic profiles of the electron 

density distribution in the NR growth direction, which depend on the ratio among the NR 

length and the number of electrons populating the conduction band of the nanostructure. In 

the case of diluted N-electron NRs, the particles are distributed in an ordered way forming a 

Wigner crystal [3]. The Coulomb energy predominates so that correlations dominate the 

electronic structure. In the opposite limit, the particles interact weakly and the kinetic energy 

dominates the Coulomb repulsion. Then, the so-called Fermi-liquid phase appears [4]. The 

transition to the Fermi liquid goes through an intermediate phase (called charge-density wave 

within the local spin-density-functional theory) which can be considered as a partially melted 

Wigner molecule [5]. In this contribution, we present a comprehensive study on the electron 

density distribution in both, NRs under applied electric fields and nanodumbbells. We show 

that two of the above-mentioned phases may coexist simultaneously in the same structure – 

but in different regions – giving rise to new phases that we refer to as mixed correlation 

phases [6]. 

[1] X. Peng, L. Manna, W. Yang, J. Wickham, E. Scher, A. Kadanich, and A. P. Alivisatos, 

Nature (London) 404, 59 (2000); S. Kan, T. Mokari, E. Rothenberg, and U. Banin, Nature 

Mater. 2, 155 (2003). 

[2] J. E. Halpert, V. J. Porter, J. P. Zimmer, and M. G. Bawendi, J. Am. Chem. Soc. 128, 12590 

(2006). 

[3] J. Planelles, M. Royo, A. Ballester, and M. Pi, Phys. Rev. B 80, 045324 (2009). 

[4] V. Filinov, M. Bonitz, and Yu. E. Lozovik, Phys. Rev. Lett. 86, 3851 (2001). 

[5] M. Koskinen, M. Manninen, and S. M. Reimann, Phys. Rev. Lett. 79, 1389 (1997). 

[6] A. Ballester, J. M. Escartín, J. L. Movilla, M. Pi, and J. Planelles, Phys. Rev. B 82, 115405 

(2010). 

141

TuP34 _______________________________________________________________ 


Simulation and Realization of Photonic Crystals in Light 

Emitting Devices 

Jakob Ebeling, Timo Aschenbrenner, Stephan Figge, and Detlef Hommel 

Institute of Solid State Physics, Univerity of Bremen, Germany 

Indium gallium nitride (InGaN) based light emitting diodes (LEDs) have been very 

successful in the blue and green spectral range. However, the light extraction efficiency 

of conventional devices suffers from the total internal reflection at the semiconductor-air 

interface due to the relatively high optical refractive index (GaN: n≈2.5) limiting the numerical 

extraction efficiency of conventional, planar LEDs based on GaN to about 4% [1]. 

To overcome this issue, different concepts have been theoretically studied and partially 

realized. Among these are encapsulation with a lower index material, surface roughening, 

thin-film LEDs and structuring the surface with photonic crystal (PC) structures, 

which are periodic variations of the refractive index at the length scale of the emission 

wavelength. The most common concept of a one-dimensional PC is a distributed Bragg 

reflector (DBR). 

Additionally to LEDs, PCs can be used to improve the properties of laser diodes. 

Commonly known are vertical-cavity surface-emitting laser diodes with DBR mirrors, 

but also distributed feedback (DFB) and DBR-based edge emitting laser diodes have 

been realized [2][3]. 

We present numerical simulations of different types of PCs and their realization on 

various structures. A one-dimensional photonic crystal grating was fabricated by focused 

ion beam (FIB) milling at the resonator ends of an edge-emitting GaN-based laser device 

forming a lateral GaN-air-DBR to enhance the reflectivity of the resonator mirrors. 

Optoelectronic measurements were made to compare devices with and without additional 

gratings. 

Moreover, green emitting InGaN-based quantum dot LED structures were grown on 

sapphire substrates with metal-organic vapour-phase epitaxy. Different two-dimensional 

PCs were structured by FIB milling as well as e-beam lithography with subsequent dry 

etching. The structure surfaces are characterized by scanning electron microscopy and 

atomic force microscopy and a comparison between the two technological methods is 

given. Optical measurements obtained by micro-photoluminescence are used to quantify 

the light extraction enhancement achieved by PC structuring. The results of the different 

structures are compared with each other and with previous simulations. 

[1] C. Wiesmann, K. Bergenek, N. Linder, and U.T. Schwarz, Laser & Photonics Review 

3, 3 (2009). 

[2] D. Hofstetter, R.L. Thornton, L.T. Romano, D.P. Bour, M. Kneissl, and R.M. Donaldson, 

Appl.Phys.Lett. 73, 2158 (1998). 

[3] J. Cho, S. Cho, B.J. Kim, S. Chae, C. Sone, O.H. Nam, J.W. Lee, Y. Park, and T.I. 

Kim, Appl.Phys.Lett. 76, 12 (2000). 

142

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Electro-optical characterization of Ti/Au-ZnTe Schottky diodes with CdTe 

quantum dots 

E. Zielony 1 , E. Popko 1 , Z. Gumienny 1 , G. Karczewski 2 



2 Institute of Physics, Institute of Physics Polish Academy of Science, al. Lotnikow 32/46, 


In this study the deep level transient spectroscopy (DLTS) and micro-Raman spectroscopy 

techniques have been applied to investigate ZnTe (p-type) – Ti/Au Schottky diodes containing 

a layer of CdTe self-assembled quantum dots (SAQDs). The reference sample was the ZnTe – 

Ti/Au diode without dots. Both samples were grown by molecular beam epitaxy technique. 

The dots were formed in the atomic layer epitaxy (ALE) growth mode by deposition of three 

monolayers of CdTe. Micro-Raman measurements confirmed the presence of CdTe layer of 

quantum dots in the investigated material. A broad band corresponding to the longitudinal 

(LO) CdTe phonon related to the QD-layer has been detected at a wavenumber of 160 cm -1 

[1] in the case of the QD sample. Another peak observed for the wavenumber of 210 cm -1 has 

been assigned to localized LO phonon associated with the ZnTe layer in both samples [1]. 

Moreover two tellurium - related bands at wavenumbers around 120 cm -1 and 140 cm -1 have 

been identified [1]. DLTS measurements for the sample with QDs reveal the presence of two 

hole-related signals with thermal activation energies equal to EH1=0.2eV and EH2=0.4eV. For 

the reference ZnTe-Ti/Au diode only the H2 signal is observed. It may be concluded that the 

H1=0.2 eV level can be assigned to the hole emission from defects accompanying quantum 

dots formation. The 0.4eV trap is attributed to the ZnTe bulk material [2]. 

[1] V. S. Vinogradov, et al., Physics of the Solid State, Vol. 50, No. 1, 2008. 

[2] E. Placzek-Popko, et al., Physica B 404 5173-5176 (2009). 

143

TuP36 _______________________________________________________________ 


Magneto-photoluminescence studies of many body scattering processes 

in two-dimensional hole gas 

J. Jadczak1 1 , L. Bryja 1 , A. Wojs 1 , G. Bartsch 2 , D.R. Yakovlev 2 , M. Bayer 2 

and M. Potemski 3 

1 Institute of Physics, Wroclaw University of Technology, Wroclaw, Poland 

2 Experimentelle Physik 2, Technische Universität Dortmund, D-44227 Dortmund, Germany 

3 Grenoble High Magnetic Field Laboratory, CNRS, Grenoble, France 

Fig. 1. PL vs magnetic field for 

the symmetric 15 nm QW. 

The 2D hole gas due to the much higher effective mass 

create a unique possibility to study a variety of many 

body scattering processes, also not observed in n-type 

systems. In this work we report on detailed lowtemperature 

(T=1.8÷4.2K), high-field (B≤28T), polarization-resolved 

magneto-photoluminescence (MPL) studies 

of 2DHG in GaAs quantum wells. In the symmetric 15 

nm wide well with a hole concentration p=1.5x10 11 /cm -2 

we detected in MPL spectra shake-up hole replicas of 

positively charged exciton (trion) on acceptor bound [1] 

and free states (Fig. 1). The former one for the first time. 

In asymmetric samples with different width 

(w=18÷30nm) and concentrations (p=1.4÷2.3x10 11 /cm -2 ) we observed an opposite process 

with hole cyclotron replicas going to higher energies with the magnetic field. The most intriguing 

effect, never reported before, was the observation of a coupling between the free and 

acceptor bound positively charged excitons (Fig. 2). The two 

states: free and bound are brought into resonance by an exchange 

of a quantum of a hole cyclotron energy in a scattering 

process with surrounding 2D holes. For the 22 nm wide 

sample the resonance is observed in magnetic field around 

B=13T. Further to our previous studies [3] we observed, that 

the essential coupling occur between free trion - X + and a 

pair of hole cyclotron replicas of the acceptor bound trion - 

CR-AX + . The coupling can be observed in photoluminescence 

spectra due to a nearly energy degeneracy of all final 

states involve in a radiative recombination. Aided with numerical 

calculations [3] we have explained the existence of 

two hole replicas as the transitions of bright and dark doublet 

states of AX + . The dark state is enabled in an optical 

transition by transfer of an access momentum to one of 2D 

Fig. 2. PL vs magnetic field 

for asymmetric 22 nm QW 

surrounding holes. In three coupling states model we have calculated energy and intensity of 

all observed PL lines and we have obtained a very good agreement with experimental data. 

The coupling is observed in spite of very small coupling constants (determined from experiment) 

only because two replicas are involved. 

[1] L. Bryja et al., Phys. Rev. B 75, 035308 (2007). 

[2] J. Jadczak et al. Acta Physica Polonica (in press) 

[3] A. Wojs, Phys. Rev. B 76, 085344 (2007); Phys. Rev. Lett. 104, 086801 (2010). 

144

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Norm. PhotoVoltaic Response (arb. Units) 

1.5 

1.0 

T = 10K 

Spin related effect in Si-MOSFETs THz Photoresponse 

Hadley Videlier 1 , Nina Dyakonova 1 , Frederic Teppe 1 , Cristophe Consejo 1 , 

Wojciech Knap 1 , Jerzy Lusakowski 2 , Daniel Tomaszewski 3 , Jacek Marczewski 3 , Piotr 

Grabiec 3 

1 Laboratoire Charles Coulomb UMR 5221 CNRS- Université Montpellier 2, 34095 

Montpellier, France 

2 Institute of Experimental Physics, Warsaw University, Warsaw, Poland 

3 Institute of Electron Technology, Al. Lotnikow 32/46, 02-668 Warsaw, Poland 

Photoresponse to sub-terahertz and Terahertz (THz) radiations in Silicon Metal Oxide 

Semiconductor Field Effect Transistors (Si-MOSFETs) has been studied previously [1-3]. The 

obtained values of responsivity and Noise Equivalent Power have shown the potential of Si- 

MOSFETs as sensitive detectors at room temperature [1]. The photovoltaic response 

dependences on the gate length and the gate bias were in good agreement with the Dyakonov- 

Shur plasma wave detection theory [4]. The detection signal results from the rectification of 

high frequency currents induced by the incident radiation in the transistor channel. The 

rectification takes place due to a nonlinear response of the gated two dimensional electron gas 

and a source-drain asymmetry. The main source of nonlinearity is the superposition of two 

radiation-induced effects: i) the modulation of the carrier density in the channel by variations 

of the gate potential and ii) current oscillations due to variations of the drain potential. 

Recently, monolithically integrated THz focal-plane arrays including antennas and amplifiers 

on a single silicon die has been designed to work at room temperature [5]. 

In this work we have studied the effect of high magnetic field on the Si-MOSFETs 

photovoltaic response subjected to sub-terahertz radiation (185-300 GHz ) at low temperature. 

Frequency (GHz) 

400 

300 

200 

100 

0 

0 3 5 8 10 13 15 

B (Tesla) 

!" # $ %$" &$ ' ( 

% ) * + ,$ - 

( . %$ 

185 GHz 

In Figure 1, photovoltaic signal is presented at 10 K 

as a function of applied magnetic field for three 

different incident frequencies. A very well 

0.5 

pronounced structure shifts to higher fields by 

0 2 4 6 8 10 

Magnetic Field (T) 

12 14 16 

increasing incident frequency. The positions of peaks 

is plotted in the inset of Fig.1 where the straight line 

follows equation f = gµ BB 

/ h and g = 2 . The calculation is in good qualitative agreement 

with experiments indicating a possible link between the observed structures in the 

photovoltaic response and a spin related phenomenon. This effect has been studied as a 

function of different parameters as temperature and applied source-drain current. However, a 

full quantitative interpretation of our results requires more complete experimental and 

theoretical developments. 

[1] R. Tauk, F. Teppe, S; Boubanga, et al. Appl. Phys. Lett. 89, 253511 (2006) 

[2] W. Knap, F. Teppe, Y. Meziani, et al. Applied Physics Letters 85 (4) 675-677 (2004) 

[3] W. Stillman, M.S. Shur, D. Veksler, S. Rumyantsev and F. Guarin, El. Lett., V43 (2007) 

[4] M. Dyakonov and M. Shur. El. Dev., IEEE Transactions on, 43(3):380–387 (1996) 

[5] E. Ojefors et al., IEEE Journal of, 44(7):1968–1976 (2009) 

145

TuP38 _______________________________________________________________ 


THz emission related to hot plasmons and plasma wave instability in 

field effect transistors 

Nina Dyakonova 1,2 , Abdelouahad El Fatimy 3 , Yahya Meziani 4 , Dominique 

Coquillat 1,2 , Wojciech Knap 1,2 , Frederic Teppe 1,2 , Petre Buzatu 1,2 , Luca Varani 5 , Hugues 

Marinchio 5 , Jeremy.Torres 5 , Pilippe Nouvel 5 

1 Université Montpellier 2, Laboratoire Charles Coulomb UMR 5221, Montpellier, France 

2 CNRS, Laboratoire Charles Coulomb UMR 5221, Montpellier, France 

3 Cardiff School of Physics and Astronomy, Cardiff University, Cardiff, United Kingdom 

4 Departamento de Física Aplicada, Universidad de Salamanca, Salamanca, Spain 

5 IES, UMR CNRS 5214, Université Montpellier 2, Montpellier, France 

The plasma waves in two-dimensional channel can be generated thermally by hot electrons 

(hot plasmons) [1] or can be due to plasma wave instability [2]. The THz emission due to 

radiative decay of non resonant hot plasmons is characterized by broad non tunable spectrum 

and a smooth onset. The mechanism plasma wave instability in a field effect transistor was 

proposed in Ref [3]. It has been shown that the electron flow in the channel should be 

unstable because of plasma wave amplification as a result of reflection from the device 

boundaries. One of characteristic features of the emission due to plasma wave instability is a 

threshold like onset. In gated part of the channel the fundamental frequency of plasma waves 

can be tuned by the gate bias. The theory developed recently [4] has shown that in realistic 

transistor geometry also oblique modes of plasma waves exist. Moreover, it has been shown a 

new type of instability related to plasma waves propagating along the gate boundary 

perpendicularly to the current direction. This instability should lead to a broad non tunable 

spectrum. 

In this work we present studies of InGaAs/InAlAs and GaN/AlGaN based field effect 

transistors .We show that origin of THz emission changes depending on the transistor 

configuration. The experimental results are supported by numerical simulations. 

We observed several types of THz emission. First, the emission onset as a function of drainsource 

voltage was of two kinds: (i) a smooth increasing of emission integrated signal and (ii) 

a threshold like appearance. For (i) case we observed non tunable broad emission spectra. The 

same results we observed for the most of the (ii) cases. However, for a transistor of special 

design we observed a voltage tunable THz emission. The gate of the transistor was covered by 

the field plate deposited between gate and drain terminals. We suppose that the plasma wave 

excitation under the gate is favored by the presence of the field plate through providing the 

needed boundary conditions 

We discuss our experimental results supposing that the emission origin depends on the 

potential distribution in the channel. In particular, simulation results show a step like behavior 

of the potential profile near the border of the gate in the case of the standard transistor and a 

smooth potential profile in the case of the transistors with a field plate. 

[1] Höpfel R. A and Gornik E. Surface Science, 142, 412-422, (1984) 

[2] El Fatimy A, Dyakonova N., Meziani Y., Otsuji T., Knap W., Vandenbrouk S.,. Madjour 

K, Théron D., Gaquiere C., Poisson M. A., Delage S., Prystawko, P. and Skierbiszewski C. , J. 

Appl. Phys., 107, 024504, (2010) 

[3] Dyakonov M. and Shur M. Phys. Rev. Lett., 71, 2465-2468. (1993) 

[4] Dyakonov M., Semiconductors, 42, 984, (2008) 

146

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A Comb-Like Shape of the Cyclotron Resonance Line 

in GaAs/AlGaAs Heterostructure 

M. Bia̷lek 1 , M. Czapkiewicz 2 , K. Fronc 2 , J. Wróbel 2 , V. Umansky 3 , 

M. Grynberg 1 , and J. ̷Lusakowski 1 


2 Institute of Physics, PAS, al. Lotników 32/46, 02-668 Warsaw, Poland 

3 Weizmann Institute of Science, Rehovot 76100, Israel 

The present work originates from a larger program devoted to investigation of plasmon 

excitations in a two-dimensional electron gas (2DEG) perturbed by a periodic potential. 

ThesamplesusedinthepresentstudywereprocessedonahighmobilityGaAs/AlGaAs 

heterostructure with the electron concentration of about 3×10 11 cm −2 . Each sample was 

supplied with two ohmic contacts and on some smples a metallic gate was deposited. The 

samples were placed in the magnetic field (up to 12 T) at 4.2 K. The source of radiation 

was a molecular laser with the lines between 70 µm and 202 µm. The signal measured 

was a photovoltage induced between the ohmic contacts. 

An overall shape of the signal as a function of the 

magnetic field is very complicated. We observe indications 

of an interference of edge magnetoplasmons, 

Shubnikov-de Haas oscillations and a cyclotron resonance 

(CR) transition. In the present communication 

we concentrate on the CR only. A typical shape of 

the signal in the vicinity of a CR is shown in Fig. 1 

and has a comb-like shape. To understand the origin 

of this multi-line structure, we have processed samples 

with different gate geometries: a flat gate without any 

periodicity, a gate of a thickness periodically changed, 

acomb-likemulti-fingergate, andameander-likegate. 

We also changed the period of the gate modulation. 

We found that 1) the comb-like shape of the CR line 

is present in all samples, with or without the gate; 2) 

photovoltage [V] 

3e-04 

3e-04 

2e-04 

2e-04 

1e-04 

5e-05 

0e+00 

-5e-05 

1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 

B [T] 

Fig. 1: Photovoltaic signal measured 

on a sample with a meanderlike 

gate illumianted with a 165 µm 

radiation. 

the distance between the components of the CR line shown in Fig. 1 does not depend on 

gate geometry and does not depend on the magnetic field. We concluded that the observed 

splitting is related to the ohmic contacts or sample edges. To verify this hypothesis 

we carried out a transmission experiment which showed a Lorentzian-like CR line thus 

confirming that “bulk” electrons are not resposible for the observerd comb-like structure. 

We discuss two mechanisms of the comb-like shape of the CR line; both of them are 

based on a theoretical work [1] which indicates that the border between a 2DEG and a 

metal (an ohmic contact in our case) is a region of an extremly strong and nonuniform 

electric field generated by the incident electromagnetic wave. In one mechanism, we 

expect splitting of the CR line due to the gradient of the electric field, as it was observed 

in investigation of gases [2]. In the other, we consider an interaction of the CR transition 

with the acoustic waves generated within the contact area by a piezoelectric effect [3]. 

This work was partially supported by a Foundation for Polish Science grant POMOST 

within EU Innovative Economy National Cohesion Strategy Program. 

[1] S. A. Mikhailov, Phys. Rev. B 83, 155303 (2011). 

[2] A. V. Rokhlenko, Zh. Eksp. Teor. Fiz. 69, 169 (1975). 

[3] N. A. Zimbovskaya, J. L. Birman, J. Phys.:Condens. Matter 12, 3337-3348 (2000). 

147

TuP40 _______________________________________________________________ 


Impurity-Related Noise in Si �-doped Single-Barrier GaAs/AlAs/GaAs 

Resonant Tunneling Devices 

Jacek Przybytek, Marta Gryglas-Borysiewicz �� 

University of Warsaw, Faculty of Physics, ��-681 Warsaw, Poland 

We have measured the current noise in single-barrier GaAs/AlAs/GaAs heterostructures 

with Si �-doping in the center of the 10nm-thick barrier for vertical mesas of diameter ranging 

from 50�m-300�m. Currents flowing through the structure ranged from a few pA to 0.1mA. 

The current noise measurements have been performed by means of crosscorrelation technique 

[1] with two home-made transimpedance amplifiers. In this technique two amplified signals 

from the sample are provided by means of two independent signal-carrying and amplifying 

channels to the analog-digital converter. The power spectral density of the sample-related 

correlated signal has been numerically calculated as a crosscorrelation spectra from two 

channels. The biasing of the sample has been achieved by applying bias voltage between 

virtual grounds of operational amplifiers used. 

Changing the bias voltage applied to the tunneling structure we change also the 

mechanism of the electron transport through the barrier [2]. For biases U0.3V the generation-recombination-like noise superimposes on the white shot noise. 

However, the Fano factor still remains below 1. In the paper we will show the impact of the 

resonant tunneling through the Si impurities on the low-frequency current noise. We will 

present the current noise spectral density measured at temperature T=4.2K for three samples 

with the same structure but different doping level in the Si-�-layer. 

The integrated low-frequency noise vs bias voltage for various samples with different �doping 

level reveals two types of noise generated in the heterostructure: 

1. for low voltages 0.3V

40th _______________________________________________________________ 


Current Driven Terahertz Detection of Quantum Cascade Laser 

Emission by Plasma Waves in Nano-Transistors 

F. Teppe 1 , C. Consejo 1 , J. Torres 2 , B. Chenaud 1 , P. Solignac 1 , Z.R. Wasilewski 3 , 

M. Zholudev 1,4 , N. Dyakonova 1 , D. Coquillat 1 , A. El Fatimy 5 , W. Knap 1 

1 L2C, UMR N°5221 au CNRS, Université Montpellier II, 34095 Montpellier, France 

2 IES, UMR N°5214 au CNRS, Université Montpellier II, 34095 Montpellier, France 

3 Institute for Microstructural Sciences, National Research Council, Ottawa, Canada 

4 Institute for Physics of Microstructures, RAS, Nizhny Novgorod, Russia 

5 

1. Introduction: The plasma waves in gated 2D electron gas have a linear dispersion law. The 

transistor channel is acting as a resonator for the plasma waves, which can reach frequencies 

in the Terahertz (THz) range for a sufficiently short gate length Field Effect Transistors 

(FETs) [1,2]. It was shown that the nonlinear properties of plasma oscillations can be utilized 

for terahertz detectors, mixers and emitters. We have demonstrated in various materials that 

the detection of THz radiations by plasma waves might be strongly modified by the 

application of a dc drain current [3,4]. We found that driving a transistor into the saturation 

region enhances the non-resonant detection and can lead to the resonant detection [5,6,7] even 

if the condition ω 0 τ >> 1 is not satisfied ( ω 0 is the fundamental plasma wave frequency and 

τ is the momentum relaxation time), since the effective decay time for plasma oscillations is 

1/ τ = 1/ τ − 2 v / L , where v is the electron drift velocity. 

eff 

2. Experimental results: In this work, we have demonstrated the detection of 3.1 THz 

radiation of a Quantum Cascade Laser (QCL) with a Field Effect Transistor (FET). The 

measured photoresponse is plotted in Fig. 1 as a function of the gate voltage for three values 

of the applied drain voltage. The signal exhibits a wide peak centred at about -0.2 V and its 

amplitude is increasing with the applied drain voltage. The position of this peak corresponds 

to the fifth harmonics of the resonant plasma mode in the transistor’s channel. The detection 

signal is attributed to the plasma wave resonance in the transistor’s channel. The applied DC 

current increases the detection amplitude as well as the quality factor of the resonant line. The 

THz system formed by the QCL source and the FET plasma wave detector has been validated 

up to liquid nitrogen temperature. 

Photoresponse (arb. units) 

2,0 

1,5 

1,0 

0,5 

0,0 

V d = 0,8 V 

V d = 0,7 V 

V d = 0,6 V 

-0,5 -0,4 -0,3 -0,2 -0,1 0,0 

Gate Voltage (V) 

[1] M. Dyakonov and M. S. Shur, Phys. Rev. Lett. 71, 2465 (1993) 

[2] M. Dyakonov and M. S. Shur, IEEE Trans. Electron Devices 43, 380 (1996) 

[3] D. Veksler, F. Teppe, AP. Dmitriev, et al. Phys. Rev. B. 73 (12): 125328 (2006) 

[4] F. Teppe, D. Veksler, V. Yu. Kachorovski, et al. Appl. Phys. Lett. 87, 022102 (2005) 

[5] F. Teppe, W. Knap, D. Veksler, et al., Appl. Phys. Lett. 87, 052107 (2005) 

[6] F. Teppe, M. Orlov, A. E. Fatimy, et al., Applied Physics Letters 89, 222109 (2006) 

[7] S. Boubanga-Tombet, F. Teppe, D. Coquillatet al., Appl. Phys. Lett. 92, 212101 (2008) 

149 

!"

TuP42 _______________________________________________________________ 


Influence of SiC substrate orientation on epitaxial graphene quality studied by Raman 

spectroscopy 

G. K pisty 1 , K.Grodecki 1,2 , W.Strupi ski 2 , A.Wysmołek 1 , R.St pniewski 1 , 

and J.M.Baranowski 2,1 

1 Faculty of Physics, University of Warsaw, Ho a 69, 00-681 Warsaw, Poland 

gk276975@okwf.fuw.edu.pl 

2 Institute of Electronic Materials Technology, Wólczynska 133, 01-919 Warsaw, Poland 

High temperature annealing, which induces sublimation of Si atoms from SiC 

substrates at high temperatures is one of the commonly used methods of graphene layers 

fabrication. It was shown that sublimation process can be successfully performed in standard 

CVD reactors used for SiC epitaxial growth. The final result of the process depends on the 

annealing temperature and time as well as any other parameters like the pressure of the noble 

gas (usualy argon) in the CVD reactor. In contrast to the fact that the influence of the argon 

pressure in the reactor on the growth rate of the graphene structures is well established [1], the 

role of the substrate orientation on the effectiveness of the process of SiC sublimation is still 

not well known. 

In the case of epitaxy use of slightly misoriented substrates favors two dimensional 

growth modes, which is crucial in the case of flat and homogeneous epilayer growth. Thus the 

use of on-axis silicon carbide samples can’t be the optimal choice for this method. It could be 

argued that misorientation of the substrate could have positive influence on out-diffusion of 

silicon atoms during SiC decomposition. 

In this communication the influence of SiC substrate orientation on epitaxial graphene 

is studied by Raman spectroscopy, which provides interesting information about strain state 

and homogeneity of the graphene structures. Here we focus our attention on the most 

prominent bands, so called the G and the 2D bands. 

The investigated samples were fabricated in the hot-wall CVD reactor Epigress VP508 at the 

temperature of 1600 0 C. Two different argon pressures of 50 mbar and 100 mbar in the reactor 

were maintained during the growth process on the 4H-SiC substrates with different 

misorientation of 0, 4, and 8 degrees. 

Micro-Raman scattering experiments were performed in back scattering geometry, 

using the 532nm line of a continuous wave Nd-YAG laser. The laser spot size on the sample 

was about 2µm in diameter. In order to collect information about strain and concentration 

homogeneity micro-Raman maps consisting of 530 points on a 2.3x2.2mm 2 sample area were 

performed. 

It was found that the average position of the 2D band, and thus biaxial strain present in 

graphene structures is not very sensitive to argon pressure on substrates with different 

misorientation. On the other hand, the 2D band average frequency increases with the 

misorientation angle. This is direct evidence that the average strain built in the graphene 

structures increases significantly with the misorientation angle. Similar behavior was found in 

the case of the 2D band broadening, for which the width is of about 30 cm -1 higher for 8 o 

misoriented substrate, as compared to the on-axis samples. The observed broadening depends 

also on the pressure of argon during the epitaxial process. 

The obtained results strongly suggest that the quality of graphene layers seems to 

decrease with misorientation of substrate. This provides additional information about 

mechanisms important in the growth of epitaxial layers by SiC sublimation. 

[1] A. Drabi ska, K. Grodecki, W. Strupi ski, R. Bo ek, K. P. Korona, A. Wysmołek, 

R. St pniewski, and J. M. Baranowski, Phys. Rev. B 81, 245410 (2010) 

150

40th _______________________________________________________________ 


Fermi edge and band-to-band recombination dynamics in n-doped 

GaAs/AlGaAs quantum well 

M. Syperek, B. Bujko, J.Jadczak, M. Kubisa, L. Bryja, and J. Misiewicz 

Institutute of Physics, Wroclaw University of Technology, 

Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland 

We performed comprehensive studies on emission properties and carrier dynamics in a 

high mobility (μ=1.8÷2.5x10 5 Vs/cm -2 ) n-doped (n=2.1÷3.4x10 11 /cm -2 ) 15 nm-wide 

GaAs/AlGaAs quantum well by means of time-integrated (PL) and time-resolved 

photoluminescence (TRPL) techniques. The low-temperature (T=4.5 K) PL spectrum reveals 

a broad emission band centered at the energy of 1.531 eV, as is shown in Fig.1. It corresponds 

to a photogenerated minority carriers recombination at zero momentum (k=0). Moreover, due 

to the higher density of a two-dimensional electron gas we are able to observe an additional 

photoluminescence feature at the high energy side of the PL peak emission. The so-called 

Fermi Edge Singularity (FES) is related to the phase-space filling of the first confined 

electronic subband [1]. Thus, weakly-k-conserving optical transitions between Fermi-sea 

electrons (at k=kf ) and localized holes in the valence subband can contribute to the PL 

spectrum as well. In the TRPL experiments in the low, non-resonant pumping regime, we 

observed the fast PL rise time of ~25 ps and the decay time of 130 ps. Both time constants are 

taken from the fit to the TRPL trace positioned at the maximum of the PL spectrum, 

corresponding to k=0 transitions. The rise time in this case is related to a hot-carrier cooling 

process whereas the decay time is tentatively attributed to a free-carrier recombination time. 

Surprisingly, the observed PL decay time taken at the energy corresponding to the FES is 

found to be comparable or even shorter than that related to the band-to-band recombination. 

We attribute this experimental finding to a small localization area of valence band holes 

which cause a considerable spread of the hole wavefunction in k–space, allowing for the 

recombination of kf>0 electrons from the edge of the Fermi sea. The photoluminescence 

dynamics can be also influenced by the non-radiative processes. 

Acknowledgement. This work has been done within the NLTK infrastructure (NLTK project 

POIG.02.02.00-00-003/08-00) 

[1] M. S. Skolnik et al, Phys. Rev. Lett. 58, 2130 (1987). 

151 

Fig.1 (left panel) TRPL 

intensity map at T=4.5 K. (right 

panel) The PL emission band 

with indicated band-to-band 

(BB) and Fermi Edge 

Singularity (FES) transitions 

with respective TRPL traces

TuP44 _______________________________________________________________ 


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F * < / 1 = = - G2G &44H" 

152

40th _______________________________________________________________ 


Interaction of epitaxial graphene with SiC substrates studied by Raman 

spectroscopy 

K.Grodecki 1,2 , J.A.Blaszczyk 3 , A.Dominiak 3 , W.Strupinski 2 , A.Wysmolek 1 , 

R.Stepniewski 1 , A.Drabinska 1 , M.Sochacki 4 and J.M.Baranowski 1,2 

1 Faculty of Physics, University of Warsaw, Poland 

2 Institute of Electronic Materials Technology, Warsaw, Poland 

3 Institute of Heat Engineering, Warsaw University of Technology, Poland 

4 Institute of Microelectronics and Optoelectronics, Warsaw University of Technology, Poland 

Epitaxial graphene on silicon carbide is emerging as an attractive process alternative to 

the graphite crystals exfoliation. Such way of growth is suitable for fabrication of large area 

graphene sheets, and is more compatible with current Si processing techniques. Commonly 

epigraphene is obtained by sublimating Si from SiC surface at high temperature (S-EG). 

Recently, it was shown that high-quality epitaxial graphene can be obtained by Chemical 

Vapor Deposition technique (CVD) [1]. 

In this communication we use Raman spectroscopy to compare epitaxial graphene 

grown by sublimation and CVD techniques on 4H-SiC (0001). 

Raman spectra of graphene-like structures consists of several bands. Here we focus on 

the 2D band which is strain sensitive. It is induced by the interaction with the substrate. 

In order to acquire more detailed information on the interaction mechanisms between 

graphene layers and the substrate additional analysis were performed. We prepared the 

micro-Raman spatial maps at room-temperature and investigated the temperature dependence 

of the 2D band frequency in the temperatures range 300-600K. 

It was found that in the case of graphene samples obtained by the sublimation method 

(S-EG layer) the mean position of the 2D line is about 60 cm -1 higher that observed on 

unstrained exfoliated layers. [2] Observed shift difference of the 2D line indicates that the S- 

EG layer is under strong compressive strain. On the other hand, for CVD-EG structure mean 

position of the 2D line was found approximately 30 cm -1 higher than for freestanding 

graphene. This observation strongly suggests that the compressive strain in the CVD-EG 

structure is about two times smaller than in the S-EG one. 

The observed difference in strain between S-EG and CVD-EG graphene is compliant 

with the data obtained from the temperature dependence of the 2D band position. 

The thermal experiments of S-EG samples revealed thermal shift of the 2D band of 

0.17 cm -1 /K. This result is in good agreement with the data reported by other groups [3]. On 

the other hand the thermal shift of 2D band for graphene samples grown by the CVD method 

remains between 0.095 and 0.034 cm -1 /K. The obtained lowest value corresponds to the 

exfoliated graphene transferred to the silicon wafers [3,4].Thus our results suggest that the Si 

sublimation growth mode always results in layers strongly pinned to the SiC(0001) substrate, 

on the other hand, the CVD growth produces layers which are only partially pinned to the 

surface. 

The interaction mechanisms responsible for different behavior of sublimated and CVD 

grown graphene layers are discussed. 

[1] W.Strupinski et al. Nano Leters (2011) 

[2] J. Röhrl,et al. Appl. Phys. Lett. 92, 201918 (2008) 

[3] N. Ferralis, et al. Phys. Rev. B 83 (2011) 

[4] I. Calizo, A. Balandin, W. Bao, F. Miao, and C. Lau, Nano Lett. 7, 2645 (2007) 

153

TuP46 _______________________________________________________________ 


Antenna-Equipped Field Effect Transistors on CdTe/CdMgTe 

Quantum Wells as Terahertz Detectors 

K. Nogajewski 1 , H. Boukari 2 , P. Kopyt 3 , W. Gwarek 3 , T. Wojtowicz 4 , 

H. Mariette 2 , M. Grynberg 1 , and J. ̷Lusakowski 1 


2 Institut Néel-CNRS, 25 Av. des Martyrs, BP 166, 38042 Grenoble, France 

3 Institute of Radioelectronics, Warsaw University of Technology, ul. Nowowiejska 15/19, 

00-665, Warsaw, Poland 


AveryhighqualityofCdTe/CdMgTequantumwellsgrownat theInstituteofPhysics, 

Polish Academy of Sciences, Warsaw, allow to consider them as promising semiconductor 

structures for terahertz applications. One of the most important factors for such applications, 

the electron mobility, can reach the values of the order of 10 5 cm 2 /Vs at liquid 

helium temperatures and thus becomes comparable to that of high quality GaAs/AlGaAs 

heterostructures. 

The idea of the present project was to use such quantum wells to process field-effect 

transistors for detection of THz radiation. A new factor of the present work, absent in 

previous studies carried out by our group, is incorporation of precisely designed antennas 

into the transistor structure. The role of an antenna is twofold. First, it increases a 

coupling of the radiation with plasma oscillations in the transistor channel thus increasing 

itssensitivity. Second,itpreciselydefinesadistributionoftheelectricfieldoftheincoming 

wave around the channel which allows to control electromagnetic forces exciting a twodimensional 

plasma in the quantum well. 

Special antennas were designed by a numerical solution of the Maxwell equations 

with a finite difference time domain method and their dimensions were optimized for the 

frequency of 2.52 THz (corresponding to a photon wavelength of 118 µm - a strong line 

of our molecular laser). Three basic geometries were considered which differed by the 

topology of the antenna shape. 

The next step was a design and fabrication of masks for the lithographic process. In 

preparation of masks we used the three basic geometries and their modifications to verify 

sensitivity of the design to perturbation of its parameters (i.e., dimensions of different 

parts of antennas and their mutual orientation). The masks were subsequently used in a 

standard UV (365nm) and deep UV (240nm) lithography performed on a few wafers of 

CdTe/CdMgTe quantum wells grown by the molecular beam epitaxy. Mesas were defined 

by a precisely calibrated dry plasma etching. Metallization of source, drain and gate 

electrodes was done with aluminum. In order to diminish the gate leakage currents a film 

of silicon dioxide was introduced bewteen the cap layer and the layer of metal forming a 

gate electrode. Ohmic contacts were prepared by etching tranches over a quantum well, 

filling it with aluminum and then exertion of a force with a hot tip. 

At the moment of the abstract submission, no THz test have yet been performed on 

fabricated transistors to compare their performance with numerical calculations. Such 

experiments are planned to be carried out in the nearest future. Both already existing 

numerical calculations and technological achievements will hopefully be supplied with 

experimental results during the Conference. 

This work was partially supported by a Polish Ministry of Science and Higher Education 

project N N515 071937. 

154

40th _______________________________________________________________ 


Effect of homogeneous electric field on exciton dispersion in wide quantum 

well 

A.D. Chegodaev 1 , D.K. Loginov 1 

1 Departament of Physics of Saint-Petersburg State University, Ulyanovskaya ul. 1, 

Petrodvorts, St.- Petersburg, Russia 

Exciton in an external homogeneous electric field was studied earlier either in bulk 

materials [1-3] or in narrow quantum wells, in which it is two-dimensional one [4-6]. These 

conditions did not allow to investigate the influence of a weak electric field on the motion of 

the exciton as a whole, because in both cases it is impossible to observe states with a large 

momentum. Such states can be observed in optical spectra of nanostructures with wide 

quantum wells, which widths are at least ten times greater than the exciton Bohr radius. 

Correspondingly, the effect of weak electric fields, which magnitude F does not exceed the 

critical value for exciton ionization, can be studied. 

In our study, we theoretically investigate the influence of an external homogeneous electric 

field on the dispersion of energy of exciton motion. The electric field is oriented 

perpendicular to the wave vector of exciton, K 

field on the spectra of light reflection from a heterostructure GaAs/AlGaAs containing a wide 

quantum well. 

We have found that the transverse external electric field induces mixing of 1s-ground and 2pexcited 

states of the exciton, which can be described by the perturbation term in exciton 

Hamiltonian: 

) 

2 2 

2 h Kˆ 

V = ( e / c ) Fr^ 

, 

m m 

where e 

m and h 

m are the effective masses of electron and hole; ^ 

r r 

F ^ . We also model the influence of such a 

e 

h 

r is the distance between an 

K ^ r r 

F r r 

|| ); Kˆ electron and a hole in the direction of the electric field vector ( ^ , ^ 

operator of the momentum of translation motion of the exciton. The mixing provides 

modification of the dependence of exciton energy on wave vector Kˆ for the 1s-ground and 

2p-excited states of exciton. In rough approximation, it can be described as a change of 

exciton translational mass due to the electric field. Preliminary calculations have shown that 

the effect is sufficient enough to be detected in optical experiments. 

References: 

h is the 

[1] V. Keldysh, JETP 33, 994 (1957) 

[2] W. Franz, Einfluss eines electrischen Felden auf eine optische Abrorptionskante, Z. 

Naturforschung 13, 484 (1958) 

[3] C. B. Duke, M.E. Alferieff, Phys. Rev. 145, 583 (1966) 

[4] D.A. Miller, D.S. Chelma, T.C. Damen, A.C. Gossard, W. Weigmann, T.H. Wood, C.A. 

Burrus, Phys. Rev. B 32, 1043 (1985) 

[5] R.T. Collins, K. v. Klitzing, K. Ploog, Phys. Rev.B, 33, 4378 (1986) 

[6] R. T. Collins, L. Vina, W. I. Wang, L.L. Chang, L. Esaki, K. v. Klitzing, K. Ploog, Phys. 

Rev.B 36, 1531 (1987) 

155

TuP48 _______________________________________________________________ 


Theoretical Analysis of Optical Losses in CdS/CdTe Solar Cells 

V.Ya. Roshko, L.A. Kosyachenko, E.V. Grushko 

Chernivtsi National University, Optoelectronics Department, 58012 Chernivtsi, Ukraine 

Since the early 2000's the mass production of solar modules based on thin-film 

CdS/CdTe has been implemented. In 2009-2010, annual capacity production of such devices of 

only one company, First Solar, exceeded 1 GW and in 2011 it is planned to exceed 2 GW [1]. 

It is predicted the rapid development of this solar energy sector, mainly because the cost of 

CdTe modules is much lower compared to those on Si wafers. The challenge facing 

researchers and technologists is increasing the efficiency of CdS/CdTe modules. After all, the 

efficiency of these modules in the production level is only about 10-11 %, while the 

theoretical limit amounts to 28-30%. The main causes of reduced efficiency of CdS/CdTe 

solar cell are optical, electrical and recombination losses. 

In the present work, the study focuses on optical losses due to absorption and reflection 

at the interfaces. Calculations have been carried out being based on the optical constants of 

materials used, the refraction index and extinction coefficient. Calculations of losses in 

glass/TCO/CdS/CdTe solar cells have been carried out taking into account reflections at the 

interfaces and absorption in the TCO (ITO and SnO2:F) and CdS layers. According to the 

Fresnel equations, when the light is at near-normal incidence, the reflection coefficient 

(reflectivity) from the interface between two contacting materials is determined by their 

refraction indexes n1 and n2. In the case of electrically conductive material, refraction index 

contains an imaginary part and can be written as n ∗ = n – iκ, where n is the refraction index, 

and κ is the extinction coefficient. The reflection coefficient from the interface is defined as 

the square of the modulus ( ∗ 1 n – ∗ 2 n )/( ∗ 1 n + ∗ n 2 ) [2]. We have calculated the short-circuit current 

density Jsc for AM1.5 total solar radiation using Tables ISO 9845-1:1992 [3]. 

It has been shown that optical losses caused by CTO layer with thickness of 200 nm are 

about 20% and 10% for ITO and SnO2: F, respectively. Thickening of the ITO layer to 500- 

700 nm leads to unacceptably high optical losses (~ 50%), while using SnO2:F the losses are 

reduced to a few percentage points only. In both cases, the presence of CdS layer, even when 

its thickness is 50 nm leads to further increase in the optical losses by approximately 10% and 

its thickening to 100 nm increases the losses by another 7-8%. The theoretical analysis allows 

us to formulate some important practical conclusions. In the case of the SnO2:F transparent 

electrode, the presence of even very thin CdS layer limits the density of short circuit current 

Jsc at ∼ 23 mA/cm 2 , and the achievement of this value in ITO/CdS/CdTe solar cell is possible 

only with an ultra-thin ITO layer. A short-circuit current density above ∼ 25 mA/cm 2 is impossible 

if to use CdS as the window layer due too narrow width of the CdS band gap (2.42 eV). 

However, it becomes possible (Jsc ≈ 26 mA/cm 2 ) for use of modified CdS films with wider 

band gap (in CTO/ZTO/CdS/CdTe devices) when interdiffusion between the CdS and 

Zn2SnO4 films "consumes" CdS film during device fabrication or using a wider band gap 

Cd1-xZnxS ternary alloy to replace CdS as the window layer. The results of calculations show 

that integrating a ZTO buffer layer into a CdTe cell with a view to modifying the CTO layer 

(rather than CdS) results in a very insignificant increase in Jsc, since the optical losses in the 

CTO are mainly due to reflection rather than absorption. 

[1] http://www.firstsolar.com/en/modules.php. 

[2] T.S. Moss, G.J. Burrel, D. Ellis. Semiconductor Optoelectronics. Butterworth Publishers, 1973. 

[3] Reference solar spectral irradiance at the ground at different receiving conditions. 

Standard of International Organization for Standardization ISO 9845-1:1992 

156

40th _______________________________________________________________ 


Anisotropy of B=0 spin splitting of holes in symmetric GaAs/Ga(1-x)AlxAs 

quantum wells 

M. Kubisa, K. Ryczko and J. Misiewicz 

Institute of Physics, Wrocław University of Technology, Wybrze e Wyspia skiego 27, 

50-370 Wrocław, Poland 

The bulk inversion asymmetry (BIA) of GaAs crystal is known to remove the spin 

degeneracy of hole states even in the absence of external fields, resulting in a wave-vectordependent 

spin splitting. The BIA splitting strongly influences hole physics in low dimensions 

and was recently observed in metal-nonmetal transitions [1], magnetic focusing experiments 

[2] and the spin-Hall effect [3]. We study theoretically the BIA splitting of heavy hole 

subbands in symmetric GaAs quantum wells with various widths and orientations. 

Calculations are performed using the standard envelope function method. The hole states are 

described in the framework of Luttinger model with added BIA terms derived using the theory 

of invariants [4]. We show that the spin splitting, proportional to k close to the subband edge, 

becomes at higher values of k nonlinear and anisotropic. Along some directions of the 

Brillouin zone the splitting decreases with k and the spin-split subbands anticross. We also 

examine the magnitude of BIA splitting as a function of well size for different growth 

directions. 

[1] S. J. Papadakis, E. P. De Poortere, H. C. Manoharan, M. Shayegan, and R. Winkler, 

Science 283, 2056 (1999). 

[2] L. P. Rokhinson, V. Larkina, Y. B. Lyanda-Geller, L. N. Pfeiffer, and K. W. West, Phys. 

Rev. Lett. 93, 146601 (2004). 

[3] J. Wunderlich, B. Kaestner, J. Sinova, and T. Jungwirth, Phys. Rev. Lett. 94, 047204 

(2005). 

[4] R. Winkler, Spin-Orbit Coupling Effects in Two-Dimensional Electron and Hole Systems, 

Springer Tracts in Modern Physics Vol. 191 (Springer-Verlag, Berlin, 2003). 

157

TuP50 _______________________________________________________________ 


Terahertz Properties of Gold Layers on GaAs 

J. Szczytko 1 , P. Arcade 2 , E. Papis 3 , A. Bara ska 3 , 

B. Pi tka 1 , and J. Łusakowski 1 

1 Faculty of Physics, University of Warsaw, ul. Ho a 69, 00-681 Warsaw, Poland 

2 CNRS-Université Montpellier2, Pl. E. Bataillon, 34950 Montpellier, France 

3 Institute of Electron Technology, Al. Lotników 32/46, 02-668 Warsaw, Poland 

In recent years there is a much interest in using field-effect transistors (FETs) for 

detection and emission of THz radiation. One of the most important group of FETs used in 

such investigation are transistors processes on GaAs/AlGaAs heterostructures. There are two 

reasons of this choice. First, a relatively high electron mobility increases a detector response 

of a GaAs/AlGaAs FET at room temperature. Second, an extreme quality of such 

heterostructures makes it possible to observe an influence of basic quantum phenomena, like 

the cyclotron resonance transition or Shubnikov - deHaas oscillations on detection at low 

temperatures and high magnetic fields. 

To understand THz properties of a transistor one should know the properties of its 

constituent parts. In particular, a question arises about properties of thin Au layers deposited 

on a semiconductor surface. Such layers are often used as a gate electrode; this is, in fact, the 

case of most of FETs investigated by us. Recently, one of our main directions of investigation 

concerns FETs processed on a high electron mobility GaAs/AlGaAs heterostructures which in 

a natural way leads to the need to understand THz properties of Au layers on a GaAs surface. 

Investigation of THz properties of such layers deposited on di_erent semiconductors is 

not a new subject. However, one can expect that these properties are strongly dependent on a 

particular fabrication process, deposition technique and other technological parameters. For 

this reason, it is important to investigate gold layers which are prepared by the method used 

subsequently in fabrication of investigated FETs. 

A series of Au layers was prepared on a (100) surface of an epi-ready semi-insulating 

GaAs by dc magnetron sputtering using Leybold L400cp system. The deposition process was 

performed in Ar+ plasma at working pressure 3 10 -3 mbar, the power of 300 W and a gas flow 

of Ar + = 100 sccm. The thickness of the Au layer changed between 50 nm and 1.5 m. Since 

the layers were too thick to allow for a transmission measurements, only reflection of light in 

the range from 1 THz to 3 THz was investigated at room temperature by a Fourier 

spectroscopy. It was found that the reflection coeffcient depends on the THz light wavelength 

and also on the Au layer thickness. To understand the dependence on the layer thickness, we 

analyzed the layers surface with a scanning tunneling microscope and a profilometer. We 

found that the surface morphology strongly depends on the layer thickness. Thus we explain 

the dependence of THz reflectivity of gold layers by their surface properties. This work opens 

the way to further investigation of THz properties of metallic gates, including studying an 

influence of the electrical polarization of the gate and properties of gates deposited on 

heterostructures with an embedded two-dimensional electron gas. 


within the EU Innovative Economy National Cohesion Program and a Polish Ministry of 

Science and Higher Education project N N515 608139. 

158

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Towards Optically Tunable Terahertz Plasmonic Detectors 

P. Sznajder, B. Pi tka, J. Szczytko, and J. Łusakowski 

Faculty of Physics, University of Warsaw, ul. Ho»a 69, 00-681 Warsaw, Poland 

Nonlinear plasma oscillations in field-effect transistors (FETs) allow to use them as 

emitters and detectors of THz radiation. There are, however, problems which await for an 

optimal solution. First, the coupling of radiation with the plasma is weak because the 

wavelength of a THz photon (~100 m) is much larger than the channel dimensions (typically 

of a few m). Second, THz performance of FETs is only weakly tuned by the electrical 

polarization of the gate. Third, a response of FETs is spectrally very broad. 

One direction of studies aims at a fabrication of voltage-tunable and resonant devices 

based on plasmons generation in a periodically modulated 2D plasma. It is known that 

deposition of a periodically structured gate enables for an optical excitation of plasmons in the 

transistor channel [1]. In recent years several groups in the world come back to this idea 

trying to fabricate either THz detectors [2] or emitters [3] in a form of a FET with a 

periodically structured gate. This method suffers from the fact that the wavevectors of excited 

plasmons are defined by the periodicity of a lithographically deposited gate which essentially 

limits tunability of the device. 

In the present work we propose an alternative approach [4] which assumes a modulation 

of the plasma with an interference pattern generated by light. This method allows to change in 

a continuous way the period of the interference fringes by a simple mechanical adjustment of 

the system and set preferable conditions for plasmons excitation. Final details of the 

experimental set up are currently under the construction, but in the meantime we proceed with 

analytical considerations of the system parameters. 

We have performed a theoretical analysis of the interference image versus the angles of 

incidence of the two interfering beams and their polarizations. In the model, two plain waves 

are superposed on the sample surface, one beam passing a linear polarizer, the other one - a 

linear polarizer and a =2 plate. The resulting image is not trivial, as it cannot be considered 

as a simple superposition of two interference images of crossed linear polarizations. One has 

to note that the light polarization in subsequent fringes is changing from one to another (e.g., 

between two different elliptical polarizations with the opposite chirality). The period of this 

oscillations is two times longer than that of the oscillations of the intensity. We show how the 

contrast of the interference pattern changes versus the angles of beams polarization and angels 

of incidence. 

Experimental verification of the theoretical analysis will be carried out on a set up with 

a Mach-Zender type interferometer and a CCD camera. A polarization system laced in front of 

the CCD allows us to probe different polarization components of the pattern. A comparison of 

the experimentally observed pattern with theoretical analysis ill allow us to optimize 

parameters of the system which is crucial for a proper design of low-temperature set-up. 



[1] S. J. Allen et al., Phys. Rev. Lett. 38, 980 (1977). 

[2] A. V. Muravjov et al., Appl. Phys. Lett. 96, 042105 (2010). 

[3] T. Otsuji et al., J. Phys.: Condens. Matter 20, 384206 (2008). 

[4] D. Weiss et al., Europhys. Lett. 8, 179 (1989). 

159

TuP52 _______________________________________________________________ 


Mobility of Holes in Nanometer Ge-on-Si p-type 

Metal-Oxide-Semiconductor Field-Effect Transistors at Low 

Temperatures 

I. Grigelionis 1 , K. Fobelets 2 , B. Vincent 3 , J. Mitard 3 , B. De Jaeger 3 , 

E. Simoen 3 , T. Y. Hoffman3, D. Jaworski 1 , and J. Łusakowski 1 

1 Faculty of Physics, University of Warsaw, ul. Ho a 69, 00-681 Warsaw, Poland 

2 Imperial College London, Exhibition Road, SW7 2BT London, United Kingdom 

3 IMEC, Kapeldreef 75, 3001 Leuven, Belgium 

I In spite of the fact that the modern electronics is based on silicon metal-oxidesemiconductor 

field-effect transistors (MOSFETs) new materials are tested in a quest for even 

faster and more powerful solutions. One of approaches concerns incorporation of germanium 

into a Si-MOSFET structure. For instance, Ge has been mixed with Si in order to induce 

strain in a Si channel which in many cases increases the carrier mobility. 

A very recent idea is to use Ge as a MOSFET channel since this material benefits from 

both higher hole and electron mobility. In such technology, a thick layer of Ge is grown on a 

Si substrate and covered with a few monolayers (ML) of Si which enables preparation of an 

oxide under the transistor gate and then the gate stack. These novel emerging devices require 

a comprehensive characterization; a part of such studies has been provided by the present 

work. 

We investigated transistors processed on a wafer with 4 ML of Si grown on Ge. The 

channel length (L) varied between 0.125 m and 10 m (10 different values of L) and its 

width was either 1.8 m or 9.8 m. About 200 transistors were tested at room temperature 

with a needle system. The threshold voltage (VTH) determined from transfer characteristics 

was found to be approximately constant for L less than about 0.5 m and equal to about -70 

mV; VTH increased to about 260 mV for L = 5 m and 10 m. 

Three transistors with L = 0.16 m, 0.19 m and 1.03 m were selected for 

magnetoresistance (MR) measurements at high magnetic fields (up to 10 T) and low 

temperatures (4.2 K). The hole mobility determined by a direct current MR (dc MR) was 

found to be about 300 cm 2 /V s and showed an increase with increasing hole concentration in 

the channel. To take into account the access resistance, we carried out also MR measurements 

with a simultaneous modulation of the gate polarization (ac MR). We developed a new 

method to determine the carrier mobility from ac MR data which was based on a solution of 

an appropriate differential equation and a one-parameter fitting. This method replaced a 

numerically unstable four parameter fitting procedure used before. The mobility determined 

from the ac MR data was about two times higher than that determined from dc R which 

allows also to estimate an influence of the access resistance on the mobility measurements. 



160

40th _______________________________________________________________ 


Vertical InAs nanowires as biological probes 

Pawel Utko 1 , Morten H. Madsen 1 , Trine Berthing 2 , Sara Bonde 2 , Claus B. 

Sørensen 1 , Karen L. Martinez 2 , and Jesper Nyg˚ard 1 

1 Niels Bohr Institute & Nano-Science Center, University of Copenhagen, 

DK-2100 Copenhagen, Denmark 

2 Department of Neuroscience and Pharmacology & Nano-Science Center, University of 

Copenhagen, DK-2100 Copenhagen, Denmark 

High-aspect ratio nanostructures, like semiconductor nanowires (NWs) and carbon 

nanofibers, can cross the membrane of a living cell without causing significant damage. 

Vertically-aligned arrays of such nanostructures might thus become a useful tool for intracellular 

delivery of biomolecules or label-free electrical measurements of intra- and 

extracellular events. 

Here, we focus on nanowires of InAs, a III-V compound semiconductor with favorable 

optical and electrical properties. We use patterned arrays of nanowires to fabricate vertical 

nanoelectrode devices. Initial results [1] indicate their low-invasiveness and biocompatibility 

when interfaced with mammalian cells. We perform electrochemical characterization 

of the InAs nanoelectrodes, followed by electrophysiological tests. 

[1] T. Berthing, S. Bonde, C. B. Sørensen, P. Utko, J. Nyg˚ard, K. L. Martinez, Small 7, 

640 (2011). 

161

TuP54 _______________________________________________________________ 


Towardsbetterlight-confinementinpillarcavities 

M.Ściesiek 1 ,T.Jakubczyk 1,2 ,W.Pacuski 1 ,A.Golnik 1 ,P.Kossacki 1 , 

C.Kruse 2 andD.Hommel 2 

1 InstituteofExperimentalPhysics,FacultyofPhysics,UniversityofWarsaw,Hoża69, 

00-681Warszawa,Poland 

2 InstituteofSolidStatePhysics,UniversityofBremen,Postfach330440,D-28334 

Bremen,Germany 

Semiconductorquantumdots(QDs)embeddedinphotonicstructurescalledmicropillarshavebeenstudiedforserevalrecentyears.Thisisbecausetheyexhibitinterestingproperties,suchashighphotonextractionefficiencyorPurcelleffect[1].Micropillarconsistof 

microcavityembeddedbetweenasystemofDistributedBraggReflectors(DBRs)onthe 

topandonthebottom[2,3].Thereisalsoplanarconfinementwhichistheeffectofetching 

thepillarsoutofthesample.WhereashorizontallythemicrocavityissurroundedbyDBRs 

thereisstillsomeleakingofphotonsverticallysincethereonlyexistsabarrierontheborderofhighrefractiveindexmicropillars’materialandlowrefractiveindexoftheairorva- 

cuum. 

DBRsfabricatedforourmicropillarshaveawidestopbandwithintherangeofQDsphotoluminescence.Neverthelessinmicropillarsthere 

existsaverythinbandpass-thecavitymode. 

ByembeddingtheQDsintothecavityonecan 

expecttheenhancementofmicroluminescence 

forthisresonantenergy.ThankstothelowvolumeofmicrocavityandhighqualityfactorQonecansignificantlyenhancelight-matercoupling.InthispaperwepresentstepstowardsobtainingmicropillarswithlatheralDBRs,which 

wouldleadtobetterconfinementoflightinside 

themicrocavity.First,10µmpillarswereetchedbyionetching.Thennextstepwasdone 

withFocusedIonBeam(FIB)anddiameterwas 

reducedto1–5µm.Attheendweobtained 

pillarswhichcanbeeasilyreachablefromthe 

side,whichallowplacingthelatheralDBRson 

them.Thespectraofmicrophotoluminescence 

Fig.1.Photoluminescencespectrafor 

micropillarswithvariousdiameters. 

confirmsthattwostepetching(ionetching+FIB)resultsinhigh-qualitymicropillars 

(Fig.1.). 

[1]A.Dousse,J.Suffczyński,A.Beveratos,O.Krebs,A.Lemaître,I.Sagnes,J.Bloch, 

P.Vosin,P.Senellart,Nature466,217(2010). 

[2]W.Pacuski,C.Kruse,S.Figge,andD.Hommel,Appl.Phys.Lett.94,191108(2009). 

[3]T.JakubczykT.KazimierczukA.GolnikP.Bienias,W.Pacuski,C.KruseD.Hommel 

Ł.KłopotowskiT.WojtowiczJ.A.Gaj,ActaPhysicaPolonicaA116,888(2009). 

162

40th _______________________________________________________________ 


Investigation of ion-implanted SiC properties by means of a light 

absorption technique 

M. Rawski, J. uk, A. Dro dziel, K. Pyszniak, M. Turek 

1 Institute of Physics, Maria Curie-Skłodowska University, Pl. M.Curie-Skłodowskiej 1, 

20-031 Lublin, Poland 

Silicon carbide is considered to be a very suitable material for manufacturing high 

temperature, high frequency as well as high power electronic devices [1]. The most interesting 

electronic and material properties appropriate for further applications have been found in the 

epitaxial layers of 4H-SiC and 6H-SiC. 

When optical and electronic properties are investigated the absorption technique becomes 

very useful. Light-wave dependent measurements of the absorption coefficient can provide 

information about the energy band gap and transitions between the valence band, conduction 

band and dopant energy levels. This, with the knowledge of the properties of unimplanted 

material gives deeper insight into the electronic energy structure of the examined implanted 

material. However, absorption measurements require of a specimen light transparency and, in 

the case of semiconductors, can only be applied to samples polished on both sides. 

In this work, the light absorption spectra of the implanted silicon carbide are presented. The 

information about the energy band gap and post-implantation disorder obtained by absorption 

edge function-fitting and deconvolution is discussed. Moreover, apart from the interband 

absorption, the transitions between the dopant states and conduction band continuum can be 

observed. The origin of these transitions is believed to be related to the Fano resonance [2]. 

[1] K. Rottner et. al., Materials Science and Engineering B61–62, 330 (1999) 

[2] P.J. Wellmann, R. Weingartner, Materials Science and Engineering B102, 262 (2003) 

163

TuP56 _______________________________________________________________ 


SiC Schottky barrier diode studied by admittance spectroscopy 

P. Kamyczek 1 , E. Placzek-Popko 1 , Łukasz Gelczuk 2 , Maria D browska-Szata 2 



2 Faculty of Microsystem Electronics and Photonics, Wrocław University of Technology, 

Janiszewskiego 11/17, 50-372 Wrocław, Poland 

Silicon carbide (SiC) is a semiconductor material with indirect bandgap. The most 

popular polytypes of SiC are 4H-SiC and 6H-SiC. Both have a wurtzite type crystal structure. 

The energy gap for SiC (Eg=3.0 ÷ 3.2 eV) is close to the energy gap of GaN (Eg= 3.4 eV) 

and therefore it is widely used as an alternative to GaN. Silicon carbide has many 

applications in micro- and optoelectronics. It is used in light emitting diodes, JFET and BJT 

transistors. SiC has low resistance and can work at high temperature. 

In this paper we report on the electrical properties of levels related to defects present 

in commercially available SiC Schottky barrier rectifiers (Cree Inc.). The motivation of this 

work were the results reported at [1]. It was found that some of the diodes exhibited 

significant reverse leakage current and proposed that such behavior may be due to the 

presence of defects leading to defect-assisted tunneling through the Schottky barriers [2]. To 

characterize deep impurities the capacitance-voltage-frequency (C-V-f) and admittance 

spectroscopy (AS) method were used. AS measurements were performed at temperatures 

ranging from 300K down to 90K and for frequencies between 2kHz to 1MHz. C-V-f 

measurements yield apparent free carrier concentration in the order of 2.2 x10 15 cm -3 

irrespective to the applied frequency. A single relaxation maximum is visible on the 

conductance/frequency versus frequency plot within the 200K-260K temperature range. The 

maximum is not sensitive to external bias. Thus it may be assumed that it is related to some 

point defect. Activation energy determined from related Arrhenius plot is equal to 

0.338±0.004eV and capture cross section 6.22x10 -15 cm 2 . Obtained results confirm DLTS 

studies run on the same samples [2]. DLTS revealed a single dominant deep-level defect of 

signature close to the one observed by us. So far there were no reports on a deep level of 

similar signature in SiC. This level is presumably responsible for afore mentioned 

discrepancies observed in I-V characteristics in the studied diodes. 

[1] Z. Synowiec, Mater. Electron., 32 (2004), 5. 

[2] L.Gelczuk et al., Materials Science–Poland - in press 

164

40th _______________________________________________________________ 


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165 

-

TuP58 _______________________________________________________________ 


Sub��10 nm Epitaxial Graphene Nanoribbon FETs 

K. Tahy 1 , W. S. Hwang 1 , J.L. Tedesco 2 , R.L. Myers��Ward 2 , P.M. Campbell 2 , 

C.R. Eddy 2 Jr., D.K. Gaskill 2 , H. Xing 1 , A. Seabaugh 1 , and D. Jena 1 

1 Dept. of Electrical Engineering, University of Notre Dame, Notre Dame, IN 46556, 

USA 

2 U.S. Naval Research Laboratory, Washington, DC 20375, USA 

This document provides instructions for preparing an abstract for “Jaszowiec” and is 

written in the format according to the guidelines given below. 

Graphene is being investigated as a promising candidate for electronic devices. For digital a 

substantial bandgap is necessary. It is possible to open a bandgap in graphene by quantum 

confinement of the carriers in patterned graphene nanoribbons (GNRs); GNRs with width W 

nm have a bandgap Eg~1.3/W eV. This implies that sub-10 nm wide ribbons can enable roomtemperature 

operation of GNRs as traditional semiconductors, but with ultimate vertical 

scaling, and still take advantage of high current drives. To date, GNRs have been fabricated 

from exfoliated graphene and operated by back gates, or nanometer scale ribbons were 

produced by ‘explosive’ methods that are not controlled and reproducible. These methods are 

not suitable for large-area device fabrication. In this work, we report lithographically 

patterned GNRs on epitaxial graphene on SiC substrates. Specifically, we show the first topgated 

GNR transistors on epi-graphene substrates that exhibit the opening of a substantial 

energy bandgap (exceeding ~0.2 eV at a ribbon width of 10 nm), respectable carrier mobility 

(700-800 cm 2 /Vs), high current modulation (10:1 at 300 K), and high current carrying 

capacity (0.3 A/mm at VDS = 1 V) at the same time. Both single GNR and GNR array devices 

are reported. 

Fig: (Left): Array of devices on large-area epitaxial graphene. (Center): Measured device 

characteristics of ~10 nm wide single graphene nanoribbon (GNR) field- effect transistor. 

(Right): Scaling to large areas - a GNR FET made of a parallel array of 30X GNRs which are 

~13 nm wide each. High modulation shows that the opening of a bandgap is robust, and can 

be scaled to multiple graphene nanoribbons. 

166

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors WeI1 

Spintronics with antiferromagnetic materials 

Tomas Jungwirth 1,2 

1 Institute of Physics ASCR, v.v.i., Cukrovarnická 10, 162 53 Praha 6, Czech Republic 

2 School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United 

Kingdom 

To date spintronics research and applications of magnetically ordered systems have 

focused on ferromagnets (FMs). There are, however, fundamental physical limitations for FM 

materials which may make them impractical to realize the full potential of spintronics. Metal 

FMs offer high temperature operation but the large magnetic stray fields make them 

unfavorable for high-density integration and metals are unsuitable for transistor and 

information processing applications. FM semiconductors on the other hand do not allow for 

high-temperature operation. We present a concept in which these limitations are circumvented 

in spintronics based on antiferromagnets. The concept is based on relativistic magnetic and 

magneto-transport anisotropy effects in nanodevices whose common characteristics is that 

they are an even function of the microscopic magnetic moment vector, i.e., can be equally 

strong in AFMs as in FMs. As a demonstration we present our experimental observation of 

>100% tunneling anisotropic magnetoresistance in a device with an IrMn AFM tunnel 

electrode [1]. As candidate high-temperature AFM semiconductors for this spintronics 

concept we introduce relativistic ab initio calculations and growth and characterization of 

bulk and epitaxial I-Mn-V compounds [2-4]. 

[1] B. G. Park, J.Wunderlich, X. Marti, V. Holy, Y. Kurosaki, M. Yamada, H. Yamamoto, A. 

Nishide, J. Hayakawa, H. Takahashi, A. B. Shick, T. Jungwirth, Nature Mat. 10, 347 (2011). 

[2] T. Jungwirth, V. Novák, X. Marti, M. Cukr, F. Máca, A. B. Shick, J. Mašek, P. Horodyská, 

P. N�mec, V. Hol�, et al., Phys. Rev. B 83, 035321 (2011). 

[3] R. J. Cava, Physics 4, 7 (2011). 

[4] F. Maca, J. Masek, O. Stelmakhovych, X. Marti, K. Uhlirova, P. Beran, H. Reichlova, P. 

Wadley, V. Novak, and T. Jungwirth (2011), arXiv:1102.5373. 

167

WeI2 _______________________________________________________________ 


Transport in topological insulators 

Ewelina M. Hankiewicz 

Institute of Theoretical Physics and Astrophysics, 

Würzburg University, Germany 

An emergent topic in physics is the discovery of new phases of matter. The quantum 

Hall state has been the first state of matter that is not classified by symmetry breaking but 

forms a topologically distinct phase, which is unaffected by small perturbations. In the last 

few years, another class of materials where topology plays a crucial role has emerged in 

physics, the so- called topological insulators [1]. Topological insulators (TIs) have a bulk 

energy gap that separates the highest occupied band from the lowest unoccupied band like in 

ordinary insulators. However, the edge (for 2D TIs) or the surface (for 3D TIs) of a 

topological insulator exhibits gapless electronic states that are protected by time reversal 

symmetry. 

In this talk I will focus on transport properties of topological insulators in two different 

regimes: (1) when the Fermi energy probes the helical edge states (counter-propagating 

gapless spin edge states) or gapless surface states and (2) when the Fermi energy is deep in 

the conduction band where the material behaves as a metal with Dirac-like band dispersion 

[2]. In both of these regimes, the Dirac-like Hamiltonian (Dirac fermions) governs the physics 

of the system. 

In the first regime, I will discuss the magnetotransport properties of the helical edge 

channels and surface states. I will show that in two-dimensional topological insulators in the 

quasiballistic regime, the spin edge channels do not mix in a magnetic field transverse to the 

quantum well, but they persist in strong quantizing fields when the Fermi level lies in the gap 

[3]. With the shift of the Fermi level into the Landau-quantized conduction band, I will 

analyze a transition between topological insulator and quantum Hall regimes. In threedimensional 

topological insulators, the magnetic field dependence of galvanic responses of 

the system shows anomalies due to broken time-reversal symmetry of the surface quantum 

Hall state. Here, I will talk about exciting novel features in magnetotransport as linear bulk dc 

magnetoresistivity and quadratic field dependence of the Hall angle [4]. 

In the second regime of doped topological insulators, I will talk about original crossover 

between symplectic and unitary classes in weak localization corrections as a function of the 

carrier concentration for a zero magnetic field [5]. 

The relevant experiments on 2D HgTe quantum wells and 3D strained HgTe will be 

discussed. 

[1] M. Z. Hasan and C. L. Kane Rev. Mod. Phys. 82 3045 (2010). X.-L. Qi, S.-C. Zhang 

arXiv:1008.2026 (2010). 

[2] B. Büttner, C. X. Liu, G. Tkachov, E. G. Novik, C. Brüne, H. Buhmann, E. M. Hankiewicz, 

P. Recher, B. Trauzettel, S. C. Zhang and L.W. Molenkamp Nature Physics 7, 418 (2011). 

[3] G. Tkachov and E. M. Hankiewicz Phys. Rev. Lett. 104, 166803 (2010). 

[4] G. Tkachov and E. M. Hankiewicz arXiv:1011.2756 (2010). 

[5] G. Tkachov, E. M. Hankiewicz arXiv:1102.4512 (2011). 

168

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors WeI3 

Progress in Nonpolar and Semipolar GaN Materials and Devices 

James S. Speck 

Materials Department, University of California, Santa Barbara, CA 93106 

speck@mrl.ucsb.edu 

Devices grown on c-plane GaN suffer from large internal electric fields due to discontinuities 

in spontaneous and piezoelectric polarization effects which cause charge separation between 

holes and electrons in quantum wells and limits the radiative recombination efficiency. 

Nonpolar GaN devices, such as in the m-plane (1100), are free from polarization related 

electric fields since the polar c-axis is parallel to any heterointerfaces. Semipolar GaN-based 

devices have reduced electric fields and in some cases, such as (1122), show a high propensity 

for Indium update for InGaN quantum wells. 

In this talk, we present work on outstanding materials issues including: morphological 

stability with special emphasis on the role of substrate orientation and growth conditions 

[1,2]; new results for dislocation-related strain relaxation in semipolar GaN-based 

heterostructures [3,4,5]; unambiguous determination of the polarization cross-over in 

semipolar InGaN/GaN heterostructures [6]; new detailed atom probe analysis of high 

performance GaN-based LEDs and laser diodes [7]. Additionally, we update progress on 

nonpolar electron devices and nonpolar and semipolar LEDs and LDs including the 

achievement of high performance true blue (� >450 nm) and true green (� >515 nm) lasers on 

m-plane and semipolar (namely, (2021)) GaN substrates [8,9]. Finally, we will present recent 

work on polarized light emission from m-plane LEDs [10] and demonstrate the first photonic 

crystal nonpolar LEDs. 

[1] R.M. Farrell et al, J. Cryst. Growth 313, 1 (2010). 

[2] R.M. Farrell et al, Appl. Phys. Lett. 96, 231113 (2010). 

[3] F. Wu et al. J. Appl. Phys. 109, 033505 (2011). 

[4] A.E. Romanov et al. J. Appl. Phys., accepted for publication (2011). 

[5] E.C. Young et al., Appl. Phys. Express, accepted for publication (2011). 

[6] H. Shen et al., phys. stat. solidi C7, 2378 (2010). 

[7] T. Prosa et al. Appl. Phys. Lett. accepted for publication (2011). 

[8] K.M. Kelchner et al, Appl. Phys. Express 3, 092103 (2010). 

[9] Y.D. Lin et al, Appl. Phys. Express 3, 082001 (2010). 

[10] S.E. Brinkley et al. Appl. Phys. Lett. 98, 011110 (2011). 

169

WeI4 _______________________________________________________________ 


Recent Progress of DERI process for growth of InN and Related Alloys 

Y. Nanishi (1,2) * , T.Yamaguchi (3) , T.Araki (4) and E. Yoon (2) 

1 Global Innovation Research Organization, Ritsumeikan University, Kusatsu, 525-8577, Japan, 

2 Department of Materials Science and Engineering, Seoul National University, Seoul 151-744, Korea, 

3 Department of Information and Comunication Eng., KogakuinUniversity, Hachioji, 192-0015, Japan 

4 Department of Photonics, Ritsumeikan University, Kusatsu, 525-8577, Japan 

* Corresponding author email: nanishi@se.ritsumei.ac.jp 

Difficulties in growing high quality InN and In-rich group III-nitride alloys hinder device 

applications of these materials to IR light sources and detectors, very high efficiency solar cells 

and high frequency transistors. Main difficulty for growth comes from its low dissociation 

temperature and high equilibrium nitrogen vapor pressure during growth. In droplets which 

form on the growing surface give another essential problem for high quality InN growth. 

A new RF-MBE growth process called DERI (Droplet Elimination by Radical Beam 

Irradiation) was proposed very recently by our group. This growth method is composed of the 

two series of growth steps with In-rich growth step and consecutive nitrogen radical beam 

irradiation step. The method enables reproducible growth of high-quality InN film with flat 

surface. In-droplet formation and elimination processes can be monitored by both in situ 

RHEED intensity variation and in situ laser beam reflection. RHEED and laser beam reflection 

techniques provide important complementary information on the InN surface structure and 

Indium adsorption, droplet formation and desorption process, respectively. 

DERI method was also applied to the growth of InGaN alloys. Distinct segregation 

phenomena were observed in this case. It has been found that the effective segregation 

coefficient is dependent on the nitrogen radical beam intensity. Using this phenomenon, 

InN/InGaN MQW structure was successfully fabricated. Thick and uniform growth of InGaN 

alloys also became possible. Possible new approach to fabricate InN based nano-structure shall 

be proposed making use of this distinct segregation phenomenon. Series of Mg doping 

experiments on InN were also carried out. For DERI process, Mg supply during DEP(Droplet 

Elimination Process) is essential for successful p-type doping. Evidences for the existence of 

free holes were successfully obtained using combinations of electrochemical capacitance 

voltage (ECV) profiling, thermo-power, XPS and electrical measurements. 

This work was supported by MEXT through Grant-in Aids for Scientific Research in Priority Areas 

“Optoelectronics Frontier by Nitride Semiconductor” #18069012 and Scientific Research (A) #21246004. 

This is also partly supported by WCU hybrid materials program of MSE at Seoul National University. 

170

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors WeO1 

Properties of TM pairs in the bulk and at the surface of GaN with and 

without Si or Mg codoping 

N. Gonzalez Szwacki 1 , J. A. Majewski 1 and T. Dietl 1,2 

1 Faculty of Physics, University of Warsaw, Warszawa, Poland 


Novel nanocharacterization methods have allowed visualizing the nanoscale 

aggregation of transition metal (TM) cations in various semiconductors, either intrinsic or codoped 

by shallow impurities [1]. This opens up new possibilities for nanomagnetism and 

nanospintronics, provided the formation of buried ferro- and/or antiferromagnetic (FM and 

AFM, respectively) nanocrystals can be controlled at the nanometer scale, possibly by n- 

and/or p-type co-doping. 

We present results of first principles calculations (employing the GGA and GGA+U 

density functional theory schemes) for GaN doped with Cr, Mn, and Fe and simultaneously 

co-doped with Si or Mg. Our results confirm that TM cations have a strong tendency to 

aggregate, i.e., to form TM-rich nanocrystals [2]. For instance, the GGA pairing energies for 

Cr, Mn, and Fe in zb-GaN are 550, 614, and 291 meV, respectively (similar values have been 

obtained for wz-GaN). We find, however, that the gain in energy upon the formation of TM 

pairs at the (0001) wz-GaN gallium surface persists only for Fe [3]. This is shown in the Fig.1 

below, where we plot the pairing energy for XY (X,Y= Fe, Si or Mg) pairs in the zb-GaN bulk 

matrix as well as at the (0001) wz-GaN surface. We see that the formation of Fe-Si pairs is 

energetically favorable both in bulk and at the surface, whereas Fe-Mg pairs may form only in 

the bulk. Si-Si and Mg-Mg pairs could form neither in the bulk nor at the surface. 

Our studies of the nominally undoped systems have revealed that the magnetic 

interaction between magnetic ions pairs has different character in the bulk crystal than at the 

surface: for example, the Mn-Mn pairs are coupled ferromagnetically in the bulk but 

antiferromagnetically at the Ga surface. In the present paper, we also demonstrate how codoping 

with Si and Mg affects the formation of TM pairs and influences the magnetic 

coupling between TM ions. Finally, we present a detailed comparison of our theoretical 

results with available experimental findings. 

The work was supported by FunDMS Advanced Grant of ERC within the Ideas 7th FP 

of EC and InTechFun (Grant No. POIG.01.03.01-00-159/08). 

[1] A. Bonanni and T. Dietl, Chem. Soc. Rev. 39, 528 (2010). 

[2] K. Sato et al., Rev. Mod. Phys. 82, 1633 (2010). 

[3] N. Gonzalez Szwacki, J. A. Majewski, and T. Dietl, Phys. Rev. B (2011), in print, 

also arXiv:1011.5968v2. 

171

WeO2 _______________________________________________________________ 


Experimental Probing of Exchange Interactions Between Localized Spins in 

a Dilute Magnetic Insulator (Ga,Mn)N� 

A. Bonanni 1 , W. Stefanowicz 2 , M. Sawicki 2 , T. Devillers 1 , B. Faina 1 , Tian Li 1 , 

T. E. Winkler 1 , D. Sztenkiel 2 , A. Navarro-Quezada 1 , M. Rovezzi 1 , R. Jakieła 2 , 

A. Meingast 4 , G. Kothleitner 4 , T. Dietl 2,3 

1 Institut für Halbleiter und Festkörperphysik, Johannes Kepler Universität, Linz, Austria 


3 Faculty of Physics, University of Warsaw, Warszawa, Poland 

4 Institute of Electron Microscopy - FELMI, Graz University of Technology, Graz, Austria 

In view of the fact that most magnetic insulators are either antiferromagnets or 

ferrimagnets, particularly intriguing is the question whether ferromagnetism is at all possible 

in dilute magnetic insulators, where carriers remain strongly localized on parent impurities or 

defects. In order to shed some light on the character of the coupling in insulating III-V DMSs 

we study Ga1-xMnxN layers (x < 3%) grown by metalorganic vapor phase epitaxy. We have 

done a comprehensive nanoscale characterization, using high resolution transmission electron 

microscopy, synchrotron radiation diffraction and absorption methods as well as high 

precision SQUID magnetometry. Structural characterization gives no evidence of crystalline 

phases other than the wurtzite structure of the host GaN. The data show that the Mn ions are 

randomly distributed over the substitutional Ga sites. 

The magnetic properties as a function of temperature, magnetic field and its orientation 

with respect to the crystal c-axis also prove the single-phase of the studied layers for x < 1%. 

No ferromagnetic-like features are detected. The whole set of experimental data for x < 1% is 

quantitatively described by the group theory of a non-interacting paramagnetic Mn 3+ ions in a 

relevant crystal field [1,2]. 

In the more concentrated case (1% < x < 3%) the sign, magnitude, and range of exchange 

couplings between pairs of Mn ions is estimated from Curie constant values analysis. Our 

findings confirm most of ab-initio predictions on the possibility of ferromagnetism in dilute 

magnetic insulators. We demonstrate that the coupling between neighboring Mn 3+ ions is 

ferromagnetic with Jnn > 10 meV and it changes to weak antiferromagnetic when the charge 

state of the Mn ions is reduced from 3+ to 2+. However the ferromagnetic coupling is found 

to be too short-ranged to lead to magnetic ordering above 1.85 K in the studied Mn 

concentration range up to 3% [3]. 

The work was supported in part by the European Research Council through the FunDMS 

Advanced Grant within the "Ideas" 7th Framework Programme of the EC, EC Network 

SemiSpinNet (PITN-GA-2008-215368), and InTechFun (POIG.01.03.01-00-159/08) from EU. 

[1] J. Gosk et al., Phys. Rev. B 71, 094432 (2005). 

[2] W. Stefanowicz et al., Phys. Rev. B 81, 235210 (2010). 

[3] A. Bonanni et al., arXiv:1008.2083v1. 

172

40th _______________________________________________________________ 


Origin of uniaxial magnetic anisotropy in (Ga,Mn)As 

M. Birowska 1 , C. Śliwa 2 , K. Milowska 1 , J. A. Majewski 1 , and T. Dietl 1,2 

1 Faculty of Physics, University of Warsaw, ul. Hoża 69, 00-681 Warszawa, Poland 

2 Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warszawa, Poland 

In this communication we present the results of theoretical studies that shed light on the long 

standing and intriguing problem of uniaxial magnetic anisotropy in (Ga,Mn)As [1,2]. In spite of 

the fact that in zinc-blende structure crystallographic directions [1,1,0] and [1,-1,0] are 

equivalent, it turns out that the magnetization (M) in (Ga,Mn)As prefers to align along one of 

these directions. 

We perform extensive studies of Mn ions pairing in GaAs based on the ab initio calculations 

in the framework of the density functional theory. We use relativistic pseudopotentials to account 

for the spin-orbit interaction and the local density approximation (LDA) for the exchangecorrelation 

density functional with the effects of non-collinear magnetism included. We use 

supercells with 64 atoms to incorporate a pair of Mn atoms in the cell (i.e., with 6.25% Mn 

concentration). Since the magnetic anisotropy is obtained from extremely small total energy 

differences for various orientations of M, we carry calculations using extraordinary high 

accuracy employing two different numerical packages (SIESTA and QUANTUM ESPRESSO). 

The results of calculations for a nearest-neighbor Mn-pair placed along [1-10] direction are 

shown in the figures below. It turns out that the system acquires maximal energy when M is 

oriented along [001] direction. The relative energy gain for M deviating from the [001] direction 

is depicted for M lying in the (001) and (1-10) planes in the first and second figure, respectively. 

It is clearly seen that the energetically most favorable direction of magnetization is along [1-10] 

one (angle 135 o ), i.e., when magnetization is parallel to the line with Mn pair. 

Further, we study the dependence the total energy on M orientation for other factors 

influencing the energetics, such as lattice relaxation of the Mn pairs, crystallographic orientation 

of Mn pairs, and stress. Further we analyze the energies of Mn pair formation and relate them to 

the magnetic anisotropy. We have just started calculations for Mn pairs at the GaAs surface to 

verify the role of the growth process. Finally, we attempt to analyze the anisotropy on the basis 

of the electronic structure changes induced by the substitution of the Mn pair into GaAs matrix. 

The work has been supported by FunDMS Advanced Grant of ERC within the Ideas 7th FP of EC, 

InTechFun (Grant No. POIG.01.03.01-00-159/08), and SemiSpinNet (Grant No. PITNGA-2008-215368). 

[1] D. Chiba, M. Sawicki, and Y.Nishitani, Nature Phys. 455, 07318 (2008). 

[2] M. Sawicki et al., Phys. Rev. B 71, 121302R (2005). 

173

WeO4 _______________________________________________________________ 


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40th _______________________________________________________________ 


Influence of composition and atomic arrangement on elastic properties of 

wurtzite InGaN and InAlN alloys 

S. P. �epkowski and I. Gorczyca 

Institute of High Pressure Physics - Unipress, Polish Academy of Sciences, ul. Soko�owska 29, 

01-142 Warszawa, Poland 

We present ab-initio study of elastic properties of wurtzite InxGa1-xN and InxAl1-xN 

alloys. Our calculations reveal that a Vegard-like approximation, i.e., linear dependence on 

the alloy content, x, cannot describe in general, the composition dependences of elastic 

constants in these materials. Moreover, we demonstrate that in InxGa1-xN and InxAl1-xN, the 

elastic constants, and consequently, the Poisson ratio and the biaxial relaxation coefficient, 

depend significantly on arrangement of In atoms. 

The elastic properties of InxGa1-xN and InxAl1-xN alloys have been investigated using 

self-consistent ab-initio calculations within a supercell model. The indium concentrations, x = 

0.125, 0.25, 0.375, 0.5, 0.625, 0.75, and 0.875, have been realized by substituting 2, 4, 6, 8, 

10, 12, and 14 Al or Ga atoms by In in a 32-atom supercell [1]. Two different atomic 

arrangements have been considered for a given x, by either distributing the In atoms as 

uniformly as possible over the supercell or by clustering the In atoms together in a part of the 

supercell [1]. For each value of x, the structures of InxGa1-xN and InxAl1-xN have been 

optimized by minimization of the total energy with respect to volume and shape of the 

supercell. Then, the supercells have been subjected to test distortions grouped in five sets in 

order to determine the values of elastic constants for the wurtzite structure [2]. The total 

energy calculations have been performed using the VASP package which is a plane-wave 

pseudopotential implementation of the density-functional theory [3]. 

Our study reveals that for alloys with a uniform distribution of In atoms, a Vegard-like 

approximation can describe the composition dependences of C12, C13, and C44 in InxGa1-xN, 

and C12, C13, and C33 in InxAl1-xN, whereas significant sublinear deviations are found for C11 

and C33 in InxGa1-xN and for C11 and C44 in InxAl1-xN. The effect of In clustering reduces C11, 

C12, and C44, and increases C33 in both InxGa1-xN and InxAl1-xN alloys. Consequently, C11, C12, 

and C44 depend sublinearly on x in clustered InxGa1-xN and InxAl1-xN alloys, whereas C33 

shows a linear and superlinear dependence on the composition in clustered InxGa1-xN and 

InxAl1-xN, respectively. The composition dependence of the bulk modulus is almost linear in 

InxGa1-xN alloys and shows a slightly sublinear character in InxAl1-xN alloys [4]. The influence 

of In clustering on the values of the bulk modulus is very small in both alloys [4]. On the 

other hand, the Poisson ratio and the biaxial relaxation coefficient depend significantly on 

arrangement of In atoms in these materials. 

This work was supported by the Polish State Committee for Scientific Research, 

Project No. NN202 010134. 

[1] I. Gorczyca, S. P. �epkowski, T. Suski, N. E. Christensen, and A. Svane, Phys. Rev. B 80, 

075202 (2009). 

[2] S. P. �epkowski and I. Gorczyca, (private communication). 

[3] G. Kresse and J. Furthmuller, Phys. Rev. B 54, 11169 (1996). 

[4] I. Gorczyca, A. Kami�ska, G. Staszczak, R. Czernecki, S. P. �epkowski, T. Suski, H. P. 

D. Schenk, M. Glauser, R. Butte, J. –F. Carlin, E. Feltin, N. Grandjean, N. E. Christensen, and 

A. Svane, Phys. Rev. B 81, 235206 (2010). 

175

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176

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors WeP1 

Thermodynamic and thermoelectric properties of (Ga,Mn)As 

Cezary liwa 1 , Tomasz Dietl 1,2 


2 Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, Poland 

This work [1], by providing a theoretical analysis of the quantities which probe directly the 

thermodynamic density of states of carriers at the Fermi level, contributes to the ongoing 

discussion whether the holes in the canonical ferromagnetic semiconductor (Ga,Mn)As reside 

in the valence band or in an impurity band. In the latter case, one expects the thermodynamic 

DOS to be significantly enhanced. 

Available experimental results are analyzed assuming that holes occupy GaAs-like valence 

bands. Allowing for Gaussian fluctuations of magnetization, the p-d Zener model describes 

correctly a critical behaviour of magnetic specific heat found experimentally in (Ga,Mn)As 

near the Curie temperature TC [2]. The magnitudes of room temperature thermoelectric power, 

as measured for GaAs:Be and (Ga,Mn)As [3], are consistent with the employed model for the 

expected energy dependencies of the hole mobility. The same approach describes also 

temperature variations of conductance specific to the Anderson-Mott localization, found for 

various dimensionality (Ga,Mn)As nanostructures at subkelvin temperatures [4]. We conclude 

that the examined phenomena do not provide evidence for an enhancement of density of states 

by the presence of an impurity band at the Fermi energy in ferromagnetic (Ga,Mn)As. 

Furthermore, we present for (Ga,Mn)As expected values of both electronic specific heat at 

low temperatures T

WeP2 _______________________________________________________________ 


Plasma-assisted Molecular Beam Epitaxy of GaN on Si (111) Substrates 

M. Sobanska, K. Klosek, Z.R. Zytkiewicz, J. Borysiuk, A. Wierzbicka, 

A. Reszka, and E. Lusakowska 

Institute of Physics, Polish Academy of Science, Al. Lotnikow 32/46, 02 668 Warsaw, Poland 

High thermal conductivity, low price and availability of large diameter wafers make 

silicon promising substrate material for epitaxial structures of group III nitrides. However, 

epitaxy of GaN on Si is difficult due to a large lattice misfit. Moreover, large difference of 

thermal expansion coefficients of GaN and Si (~116%) causes thermal strain that leads to 

cracking of GaN layers thicker than ~1 µm if strain compensating interlayers are not used. 

We report on growth of GaN layers on (111) silicon substrates by plasma assisted MBE 

(PAMBE). Riber Compact 21 system with elemental sources of Al, Ga, In, Si, and Mg was 

used for the growth. Active nitrogen was supplied from an Addon RF plasma source equipped 

with an optical Si sensor that measures the light intensity emitted by the nitrogen plasma in 

the wavelength range of 750 to 850 nm. We have shown that the sensor output signal is a 

direct measure of the amount of active nitrogen species produced by the RF source and 

available for growth. Thus, the use of the sensor assures precise control of the growth rate. 

In this work we show that before epitaxial growth of GaN an AlN buffer layer must be 

deposited on Si first. It helps to accommodate lattice mismatch with the substrate and protects 

the Si wafer against its contact with gallium that would lead to a catastrophic dissolution of 

the substrate and to growth of polycrystalline material. Additional AlN interlayers are inserted 

into GaN to compensate large tensile thermal strain that appears in GaN upon post-growth 

cooling due to mismatch of thermal expansion coefficients of GaN and Si. They also 

efficiently block diffusion of Si and O impurities from the substrate into the layer. 

Optical microscopy, scanning electron microscopy, transmission electron microscopy 

photoluminescence, and high resolution X-ray diffraction were used to study how 

crystallographic perfection of the layers depends on growth parameters. In particular, we 

focused on preparation of the substrate (in-situ thermal oxide desorption vs. ex-situ chemical 

treatment), procedure of growth initiation (Al or N first), value of III/V ratio and an optimal 

design of the AlN/GaN stack. 

GaN 

AlN 

GaN 

AlN 

Si(111) 

3,2 3,3 3,4 3,5 

energy [eV] 

Cross-section of GaN on Si structure: SEM (a) and TEM (b) image; (c) PL of the sample. 

This work was partly supported by the European Union within European Regional 

Development Fund, through grant Innovative Economy (POIG. 01.03.01-00-159/08 

InTechFun). 

178 

intensity (Counts) 

3200 

3000 

2800 

2600 

2400 

2200 

2000 

1800 

1600 

1400 

1200 

1000 

800 

2011-02-23 

exc 300 nm 

T 15 K

40th _______________________________________________________________ 


Role of Interface Carrier Transport in Electrical Characteristics of Light 

Emitting Devices Based on Heterostructures 

Joanna Płaziak, Jakub Higersberger, and Jacek A. Majewski 

Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, ul. Hoża 69, 

PL-00-681 Warszawa, Poland 

In this communication we present novel procedure to treat quantum effects in transport 

of carriers in optoelectronic devices based on heterostructures. Carrier transport in certain 

regions of Light Emitting Diodes (LEDs) and Laser Diodes (LDs) is treated quantum 

mechanically and these regions are smoothly embedded in the standard transport simulator for 

devices based on semi-classical drift-diffusion equations. Within the developed new scheme, 

we study the current-voltage characteristics of the typical arsenide and nitride structures. 

Correct modeling of carrier transport is a prerequisite of the understanding and ability 

to design new structures for optoelectronics. Traditional transport simulation tools use semiclassical 

drift-diffusion model to describe transport over the entire device, including the 

interfaces. This approach is based on the assumption that quasi-Fermi levels are continuous 

through the whole region of the device, also at the interfaces of heterojunctions. On the other 

hand, Monte Carlo transport simulations have demonstrated [1] that quasi-Fermi levels do not 

have to be continuous at interfaces and the transport 

over/through a barrier is not governed by physics 

included into drift-diffusion model. Therefore, 

quantum mechanical effects responsible for the 

physical mechanisms of transport in 

heterostructures have to be taken into account. 

However, the full quantum mechanical modeling of 

transport in diffusive regime for whole device (i.e., 

over the range of micrometers) is not possible yet. 

Therefore, in our studies we have followed previous 

suggestions to describe carrier transport quantum 

10 

0,0 0,2 0,4 0,6 0,8 

-5 

10 -4 

10 -3 

10 -2 

10 -1 

10 0 

10 1 

10 2 

10 3 

10 4 

10 5 

10 6 

10 7 

10 8 

10 9 

10 10 

mechanically only in the regions containing heterostructures and quantum wells [1]. We 

consider one of dominant transport mechanisms of quantum mechanical origin for 

heterostructures, namely, the tunneling of electrons through the narrow barriers of the 

quantum well systems. In other parts of the device, the semi-classical transport mechanism is 

considered, as implemented in the state-of-the-art nextnano 3 code [2]. 

The role of tunneling effects is illustrated for the GaAs/AlGaAs/GaAs system with a 

single barrier of two highs (0.1 and 0.3 eV) in the figure. For both structures, we have 

calculated the current-voltage [i.e., I(V)] characteristics (i) employing the drift diffusion 

approach [2], and (ii) calculating I(V) for tunneling process quantum mechanically [3]. For 

small barrier high, the drift diffusion current dominates over the tunneling current, whereas 

for higher barrier the situation is just the opposite, the transport through the barrier is 

completely determined by the tunneling process and neglecting it leads to totally wrong I(V) 

characteristics. The tunneling currents turn out to be also extremely important in structures 

with multiple barriers. 

[1] D. Schroeder, Modeling of Interface Carrier Transport for Device Simulation, 

Springer-Verlag, Wien, 1994. 


[3] Y. Ando, and T. Itoh, J. Appl. Phys. 61, 1497 (1986). 

179 

Current Density (A/cm 2 ) 

10 11 

Voltage (V) 

Drift-Diffusion model 

Tunneling effects 

DV = 0.1eV 

DV = 0.3eV 

DV

WeP4 _______________________________________________________________ 


Influence of crystal structure and hole concentration on 

magnetic anisotropy of GeMnTe 

Andrzej ̷Lusakowski 1 , Piotr Bogus̷lawski 1,2 , Wojciech Knoff 1 and 

Tomasz Story 1 

1 Institute of Physics, PAS, Al. Lotników 32/46, 02-668 Warszawa, Poland 

2 Institute of Physics, University of Bydgoszcz, ul. Chodkiewicza 30, 85-072 Bydgoszcz, 

Poland 

GeTe is a narrow gap IV-VI semiconductor crystallizing at high temperatures in the 

cubic NaCl structure. At temperatures below T0 = 670 K, a structural transition takes 

place to the rhombohedral phase with the angle characterizing the unit cell α ≈ 88.3 ◦ . 

In addition, the Ge and Te sublattices are displaced relative to each other along [111] 

direction by a vector τa0(111), where the lattice constant a0=5.987 ˚A and τ ≈ 0.02. 

This displacement causes GeTe to be ferroelectric. The above features characterize also 

Ge1−xMnxTe mixed crystals, with the difference that the critical temperature T0(x) decreases 

with the increasing manganese content x. Manganese ions introduce in GeMnTe 

local magnetic moments and this IV-VI diluted magnetic semiconductor exhibits ferromagnetic 

transition with the Curie temperature TC(x) up to 200 K. The simultaneous 

presence of ferromagnetic and ferroelectric order (ferroicity) makes this compound very 

interesting for possible applications. 

Recently, magnetization and ferromagnetic resonance (FMR) measurements were performed 

on monocrystalline layers of Ge1−xMnxTe grown on BaF2 (111) substrate as well 

as on polycrystalline, layered Ge0.9Mn0.1Te microstructures [1, 2, 3]. The experiments 

probed the magnetic anisotropy energy in the ferromagnetic state. One of the striking 

results is that in monocrystalline layers the easy axis of magnetization is perpendicular to 

the layer while the usual in-plane easy axis due to dipolar interactions (shape anisotropy) 

is observed in polycrystalline microstructures and is partially recovered in GeMnTe layers 

upon annealing. The analysis of the angle dependence of the FMR resonance field yielded 

for Ge0.85Mn0.15Te layer perpendicular magnetic anisotropy field HA=0.2 T. 

In this work we present the results of first principles calculations of magnetic anisotropy in 

distorted GeMnTe crystal and compare them with the experimental data for Ge1−xMnxTe 

layers. The calculations were done for an eight atom supercell containing three Ge, one 

Mn and four Te atoms, it means we consider Ge0.75Mn0.25Te mixed crystal. The magnetic 

anisotropy energy was assessed by calculating the total crystal energies for different orientations 

of magnetization relative to the crystal axes. The calculations were done for three 

rhombohedral angles α equal to 88 ◦ , 90 ◦ (cubic lattice) and 92 ◦ , and for the ferroelectric 

sublattice displacement 0 ≤ τ ≤ 0.025. Our model simulates the experimental situation 

of GeMnTe/BaF2 layer thermally strained along [111] growth direction. We studied also 

the influence of hole concentration, p, on the magnetic anisotropy energy. 

The results indicate a very strong dependence of anisotropy energy on α, τ and p. The 

main conclusion is that for the parameters characterizing the experimentally investigated 

samples the theoretical easy magnetic axis is perpendicular to the layer’s plane, in agreement 

with our measurements. Analysis of the underlying mechanism will be provided. 

We also discuss the role of single ion anisotropy. 

[1] W. Knoff et al. Mat. Sci. Poland 25, 295 (2007), phys. st. sol. (b) 2011 - in print 

[2] Y. Fukuma et al. Appl. Phys. Lett. 93, 252502 (2008) 

[3] H. Przybylińska et al. Spintech V, Cracow, Poland (2009) 

180

40th _______________________________________________________________ 


High-resolution study of valence band maximum for (GaMn)As 

I. Ulfat 1,2,3 , L. Ilver 1 and J. Kanski 1 

1 Department of Applied Physics, Chalmers University of Technology, SE-41296 Goteborg, 

Sweden 

2 MAX-lab, Lund University, SE-22100 Lund, Sweden 

1 Department of Physics, University of Karachi, Karachi-75270, Pakistan 

The anticipation of utilizing (GaMn)As for constructing electronic devices where magnetic 

elements (for logic and/or memory) are integrated in the semiconductor structure has 

motivated intensive investigation of this system over the last two decades. Whether practical 

realization of spintronic devices based on this system will happen is still an open question 

because the ferromagnetic state is found only at temperatures below 200 K [1]. One issue of 

recent debate [2] concerns the electronic states involved in the ferromagnetic ordering, 

specifically whether these states are holes in the GaAs valence band, or belong to an impurity 

band. 

In this report we present recent data on the electronic structure near the valence band 

maximum, obtained at the undulator beamline (BL-I3) at the synchrotron radiation laboratory 

MAX-lab. (Ga,Mn)As samples with varying Mn concentrations were prepared in a new online 

MBE system, and were transferred in UHV to the photoelectron spectrometer. Our results 

show that already at 0.5% Mn concentration a characteristic narrow band is formed near the 

center of the Brillouin zone. This band becomes increasingly accentuated with increasing Mn 

concentration, as shown in Fig. 1. 

a) 

b) 

Fig 1: VBM for clean GaAs(100 (a) and (Ga,Mn)As with 0.5% (b) and 1% Mn (c). 

Our results will be discussed in relation to previous valence band studies and to the different 

theoretical models of the valence band structure of (Ga,Mn)As. 

References: 

[1] L. Chen et al., Appl. Phys. Lett. 95, 182505, (2009) 

[2] see e.g. S. Ohya et al., Nat. Phys. 7, 342–347 (2011) 

181 

c)

WeP6 _______________________________________________________________ 


Low temperature grown (Zn,Co)O studied in the band-gap spectral region 

J. Suffczyński 1 , K. Gałkowski 1 , P. Kaźmierczak 1 , J. Papierska 1 , M. Furman 1 , 

W. Pacuski 1 , A. Golnik 1 , A. M. Witowski 1 , J. A. Gaj 1 , W. Stefanowicz 2 , M. Sawicki 2 , 

M. Łukasiewicz 2 , E. Guziewicz 2 , M. Godlewski 2 

1 Institute of Experimental Physics, Faculty of Physics,University of Warsaw, Warsaw, Poland 


Increasing interest in the low temperature grown semimagnetic semiconductors results 

from the perspective of their possible applications in spintronics and electronics, e. g. in a 

construction of 3D non-volatile memories.[1] 

The work presents the results of magnetooptical investigation of nonuniform 

(Zn,Co)O layers grown at temperatures in the range from 160 to 300 ºC by Atomic Layer 

Deposition (ALD) on Si buffer. The concentration of Co, determined by SIMS and EDS 

techniques, ranged up to 20 %. Rapid Thermal Annealing was performed on the selected 

samples at temperatures from 300 to 800 ºC. As shown by AFM and SEM characterization 

the samples exhibit polycrystalline structure.[2] Depending on the sample, either 

paramagnetic or ferromagnetic response was observed in magnetometry measurements. 

Reflectivity and photoluminescence (excitation at 400 nm) measurements are carried 

out in UV and visible spectral range at magnetic fields up to 7 T (Faraday configuration) at 

temperature 1.5 K and 300 K. Far- and mid-infrared reflectivity is also measured at 300 K. 

No distinct transitions and no meaningful splitting in magnetic field are evidenced in 

the near band gap spectral region of the reflectivity spectra. This indicates that the structures 

are highly inhomogeneous and that exchange interaction with individual Co ions does not 

induce splitting of bands. This observation shows that Co ions are aggregated in Co-rich 

regions and that concentration of individual Co ions is negligible, what is consistent with the 

lack of emission related to individual Co ions. 

Reflectivity spectra in the band gap region are strongly affected by Fabry-Perot 

interferences resulting from multiple reflections of the light in the thin film. The interferences 

are gradually damped in a wide spectral region when Co concentration increases. This 

indicates that absorption related to Co-rich precipitations increases and/or sample crystalline 

quality decreases with increasing Co doping. On application of the magnetic field the 

reflectivity spectra undergo a net splitting (0.25 meV over the range of 7 T) without an 

effective change of the spectrum shape. This is attributed to the field dependent contribution 

to the absorption of Co precipitates modifying the refractive index of (Zn,Co)O. 

The results of infrared reflectivity are modeled taking into account dynamical dielectric 

function including phonons and plasma of carriers. Carrier concentration is found to be 

typically in the range from 1 to 40 *10 16 cm -3 . Plasmonic absorption egde not observed in the 

case of some samples is recovered after annealing. 

Annealing of the samples recovers Fabry-Perot interferences, indicating that sample 

absorption is decreased and/or the crystal quality of the layers is improved. This results from 

Co-rich regions spatial redistribution, i.e. their diffusion towards the buffer-film interface, as 

confirmed by SIMS measurements. No emission from isolated Co ions even after annealing is 

observed indicating a negligible diffusion of the individual ions out of the Co precipitations. 

[1] E. Guziewicz et al., Acta Phys. Pol. 116, 814 (2009). 

[2] M. Łukasiewicz et al., Phys. Status Solidi B 247, 1666 (2010). 

The work was supported by FunDMS Advanced Grant of ERC within the Ideas 7th FP of EC, NCBiR 

project LIDER, and InTechFun (Grant No. POIG.01.03.01-00-159/08). 

182

40th _______________________________________________________________ 


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WeP8 _______________________________________________________________ 


Symmetry of the top valence band states in GaN/AlGaN 

quantum wells and its influence on the polarization of emitted 

light 

W. Bardyszewski 1 and S.P. ̷Lepkowski 2 

1 Institute of Theoretical Physics, University of Warsaw, ul. Ho˚a 69, 00-681 Warszawa, 

Poland 

2 Institute of High Pressure Physics, “Unipress”, Polish Academy of Sciences, 

ul. Soko̷lowska 29/37, 01-142 Warszawa, Poland 

We show theoretically that for narrow GaN/AlGaN quantum wells, lattice matched 

to GaN substrate/buffer and grown along the c-crystallographic direction the topmost 

valence subband symmetry depends critically on such parameters as quantum well thickness 

and barrier composition. This effect determines polarization of the emitted light. It 

is noted that the symmetry of the topmost valence band level is sensitive to the values 

of the D3 and D4 deformation potentials and can be employed in verification of existing 

literature values of these parameters. 

Group III-N semiconductors crystallizing in the wurtzite structure have complex valence 

band structure in the vicinity of the Γ point consisting of three subbands corresponding 

to the heavy hole (HH), light hole (LH) and the crystal-field split-off subband 

(CH). In the unstrained bulk GaN and InN the top subband is of HH character whereas in 

the bulk AlN the sequence of subbands is inverted with topmost light hole subband. This 

inversion obviously is present in AlGaN alloys. Combining two materials such as AlGaN 

and GaN in one quantum well system gives an opportunity to modify the structure of 

the top of the valence band states. Quantum structures built with these semiconductor 

materials, conventionally grown along the c-crystallographic direction of the wurtzite 

structure, are used to produce ultraviolet light emitters and high power electronic devices 

[1]. In most cases the character of the topmost valence subband in GaN/AlGaN quantum 

wells is usually of HH type. However in very narrow quantum well a reordering of the top 

valence subbands occurs resulting in the LH subband at the top of the valence band [2]. 

The description of this phenomenon requires taking into account the large biaxial strains 

and huge built-in electric fields (caused by piezoelectric and spontaneous polarizations) 

which are present in these structures and lead to dramatic changes in the electronic states 

of the conduction and valence bands [1]. We provide the quantitative description of this 

problem in the framework of the k ·p method demonstrating how sensitive is the ordering 

of the topmost valence levels to the exact values of relevant parameters, in particular 

the deformation potentials D3 and D4 [3]. In order to illustrate the effect of reordering 

of the topmost valence subbands on polarization of emitted light, we present theoretical 

excitonic absorption and emission spectra for various quantum well structures. 

This work was supported by the Polish State Committee for Scientific Research, 

Project No. NN202 010134. 

[1] H. Morkoc, Nitride semiconductors and devices, (Springer-Verlag, Berlin Heidelberg 

New York, 1999). 

[2] P.A. Shields, R.J. Nicholas, N. Grandjean, and J. Massies, Phys. Rev. B 63, 245319 

(2001). 

[3] Q. Yan, P. Rinke, M. Scheffler, and C.G.V. de Walle, Appl. Phys. Lett. 95, 121111 

(2009). 

184

40th _______________________________________________________________ 


Tunnelling effects in (Ga,Mn)As based heterostructures 

D. Sztenkiel 1 and T. Dietl 1,2 


2 Faculty of Physics,Warsaw University,Warszawa, Poland 

There is considerable debate about whether the holes reside in narrow impurity-band 

orinaweaklyperturbedvalencebandinthedensityregimerelevanttotheferromagnetism 

of (Ga,Mn)As. For example, in a recent articles Ohya et al. [1,2] presented comprehensive 

investigations of tunnelling spectroscopy for a series of layer structures involving high 

quality Au/(Ga,Mn)As/AlAs/GaAs:Be tunnel junctions [1]. The oscillations observed in 

the d 2 I/dV 2 -V characteristics for negative bias at the (Ga,Mn)As side was attributed to 

resonant tunnelling involving valence band subbands in (Ga,Mn)As quantum well. The 

authors concluded, that the Fermi level in this compound exists in the band gap, weakly 

perturbedvalencebandremainsseparatedoftheMnimpuritybandanditsexchangesplitting 

is very small even in samples with high Curie temperatures. These findings suggest 

that the Zener double-exchange mechanism is probably applicable for GaMnAs. However, 

we would like to propose an alternative interpretation [3] assuming that pd Zener model 

can properly describe properties of ferromagnetism in p-type Mn-doped semiconductors. 

In the (Ga,Mn)As/AlAs/GaAs:Be heterostructures, owning to a modulation doping effect, 

an interfacial region in GaAs:Be is depleted of holes. By applying a negative bias, a 

flat band condition is reached at V ≈ 0.1 V, followed by hole accumulation in GaAs:Be. 

Due to a relatively low acceptor density and disorder, weakly broadened two-dimensional 

(2D) hole subbands are then formed in non-magnetic GaAs:Be. Accordingly, nonmonotonic 

dependence of d 2 I/dV 2 on V can be attributed to resonant levels created at the 

AlAs/GaAs:Be interface. In fact, formation of 2D hole subbands in the accumulation 

layer was already observed in p-type GaAs based heterostructures [4]. At the same time, 

the observation of resonant levels in (Ga,Mn)As by tunneling spectroscopy is hampered 

by high hole relaxation rates in this alloy. Thus, the proposed model allows explaining 

why the exchange splitting and a significant contribution of the impurity band were not 

observed in the tunnelling spectra. 

The work was supported by FunDMS Advanced Grant of ERC within the Ideas 7th 

FP of EC and InTechFun (Grant No. POIG.01.03.01-00-159/08) 

[1] S.Ohya, K. Takata and M. Tanaka, Nature Phys. (2011). 

[2] S. Ohya, I. Muneta, P. Nam Hai and M. Tanaka, Phys. Rev. Lett. 104, 167204 (2010). 

[3] T. Dietl and D. Sztenkiel, arXiv:1102.3267. 

[4] T. Hickmott, Sol. St. Comm. 76, 315 (1990); R. Hayden, et al., Phys. Rev. Lett. 

66, 1749 (1991). 

185

WeP10 _______________________________________________________________ 


Modelling of Ordering Phenomena in Nitride Semiconducting Alloys 

Michał Łopuszyński 1 and Jacek A. Majewski 2 

1 Interdisciplinary Centre for Mathematical and Computational Modelling, University of 

Warsaw, Pawińskiego 5A, 02-106 Warsaw, Poland 

2 Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, 


AlN, GaN and InN together with their alloys form important group of semiconducting 

materials, particularly well suited to applications in optoelectronics. This is mainly due to 

their electronic properties – all of them have direct band gaps, being respectively 

DEAlN = 6.3 eV, DEGaN = 3.5 eV, DEInN = 0.8 eV. This large spread of band gaps, in principle, 

enables for fabricating devices operating in very broad spectral range from UV through the 

whole visible region to the IR part. This, however, requires fabricating mixtures of AlN, GaN 

and InN. Unfortunately, physics of these alloys is currently not sufficiently well understood. 

Especially, the issue of In clustering attracted a lot of attention, as it is believed to have 

important consequences for luminescence of the samples [1]. The literature reports different 

experimental findings concerning occurrence of these phenomenon, e.g. transmission electron 

microscopy revealed considerable inhomogeneity of In concentration [2], whereas 3D atomic 

probe measurements show uniform distribution of In atoms in light emitting quantum wells 

[3]. Therefore, the modelling of structural properties of nitride alloys could provide here a 

valuable insight, useful both from scientific and practical viewpoint. 

In this work we present Monte Carlo modelling scheme based on the Keating model [4] 

and its recent parameterization for nitrides [5]. We carry out our simulations for the zinc 

blende phase. Our approach enables for studying the composition and temperature influence 

on homogeneity and ordering phenomena in the nitride alloy samples. To obtain quantitative 

picture Warren-Cowley short range order parameters G (i) are used, and their dependence on 

composition and temperature is calculated. Except the bulk alloys, we study also strained 

epitaxial layers within elastic accommodation of strain regime. This allows investigation how 

the degree of ordering is influenced by the presence of substrate and the associated misfit 

strain. It turns out that the presence of large misfit strains can facilitate the development of 

long range order in the produced nitride layers. For examined substrates, we also estimate 

critical thickness as a function of layer alloy composition using Matthews and Blakeslee 

model [6]. 

[1] S. Chichibu, T. Azuhata, T. Sota, and S. Nakamua, Appl. Phys. Lett. 70, 2822 (1997). 

[2] M. D. McCluskey, L. T. Romano, B. S. Krusor, D. P. Bour, N. M. Johnson, and S. 

Brennan, Appl. Phys. Lett. 72, 1730 (1998). 

[3] Mark J. Galtrey, Rachel A. Oliver, Menno J. Kappers, Colin J. Humphreys, Debbie J. 

Stokes, Peter H. Clifton, and A. Cerezo, Appl. Phys. Lett. 90, 061903 (2007). 

[4] P. N. Keating, Phys. Rev. 145, 637 (1966). 

[5] M. Łopuszyński and J. A. Majewski, J. Phys.Condens. Matter 22, 205801 (2010). 

[6] J. Matthews and A. Blakeslee, J. Cryst. Growth 27, 118 (1974). 

186

40th _______________________________________________________________ 


Infrared Spectroscopy of GaN Crystals Obtained by Ammonothermal 

Method 

M. Welna 1 , R. Kudrawiec 1 , M. Motyka 1 , J. Misiewicz 1 , R. Kucharski 2 , M. Zając 2 , 

R. Doradziński 2 , and R. Dwiliński 2 

1 Institute of Physics, Wroclaw University of Technology, Wybrzeże Wyspiańskiego 27, 


2 AMMONO sp. z.o.o., Czerwonego Krzyża 2/31, 00-377 Warsaw, Poland 

robert.kudrawiec@pwr.wroc.pl 

The recent progress in the growth of truly bulk GaN crystals by ammonothermal method [1] 

allows a mass production of GaN substrates with various crystallographic orientations 

including non-polar [2] and semi-polar substrates [3] of various conductivity. It was observed 

that the color and transparency of GaN substrates obtained by this method change 

significantly with the intentional doping. For many application the transparency of GaN 

substrates is a very important issue. Such a situation takes place for intersubband devices 

operating in mid-infrared spectral range where GaN templates grown on sapphire substrates 

can be less transparent. In this work we measured reflectance and transmittance for nominally 

undoped and intentionally doped GaN substrates in visible, infrared and mid-infrared spectral 

regions. It was clearly observed that in the mid-infrared spectral range the transparency of 

undoped and slightly doped GaN substrates is excellent for applications in devices operating 

on intersubband transitions. In addition, it was observed that the color of GaN substrates 

results from the defect related absorption. The intensity of a given absorption band changes 

with the concentration of intentional doping. High transparency and no colors of GaN 

substrates can be achieved when the intentional doping is suitably tuned. In this work we will 

discuss the origin of light absorption in the transparency region of GaN crystals. In addition, 

we will discuss the phonon-related absorption in the mid-far infrared spectral region. Some 

examples of transmission spectra measured for various GaN substrates in the mid-far infrared 

spectral region are presented below. 

Light transmission, I/I 0 

1 

0.1 

0.01 

1E-3 

Increase of free 

electron concentration 

Absorption on free electrons 

n-type GaN 

SI GaN 

1E-4 

2 4 6 8 10 12 14 16 18 

Wavelength (mm) 

Light transmission, I/I 0 

1.0 

0.8 

0.6 

0.4 

0.2 

w TO w TO 

[1] R. Dwiliński, et al., J. Cryst. Growth 312, 2499 (2010). 

[2] R. Kucharski, et al., Appl. Phys. Lett. 95, 131119 (2009). 

[3] R. Kucharski, et al., Appl. Phys. Express 3, 101001 (2010). 

2w TO 2w TO 

AMMONO GaN 

HVPE GaN 

GaN/Al 2 O 3 

0.0 

0.05 0.10 0.15 0.20 0.25 0.30 

187 

Energy (eV)

WeP12 _______________________________________________________________ 


Micro-photoluminescence of GaInNAs layers: Thermal quenching of 

individual exciton lines 

M. Latkowska 1 , R. Kudrawiec 1 , G. Sęk 1 , J. Misiewicz 1 , J. Ibáñez 2 , M. Henini 3 , 

and M. Hopkinson 4 

1 Institute of Physics, Wrocław University of Technology, Wybrzeze Wyspianskiego 27, 


2 Institut Jaume Almera, Consell Superior d’Investigacions Científiques, 

08028 Barcelona, Spain 

3 School of Physics and Astronomy, University of Nottingham, 

Nottingham NG7 2RD, United Kingdom 

4 Department of Electronic and Electrical Engineering, University of Sheffield, 

S3 3JD Sheffield, United Kingdom 

GaInNAs (with ~2% nitrogen and ~20% indium content) is widely investigating due to their 

promising applications in optoelectronic devices including solar cells and GaAs-based lasers 

operating in the fiber optic telecommunication windows. Unfortunately, the structural quality 

of GaInNAs alloys deteriorates significantly after the nitrogen incorporation. This leads to a 

strong carrier localization at low temperatures. It is especially demanding to explore the origin 

of this phenomenon and determine its characteristic properties like the activation energy for 

the localized carriers. Currently it is widely accepted that broad PL band, which is attributed 

to recombination of localized excitons, is composed of sharp lines related to individual 

excitons. An evidence for this interpretation has been found in near-field PL [1] as well as in 

micro-PL [2] measurements. Unfortunately, the exact nature of this lines is still unknown and 

controversial. In this work the authors applied the temperature-dependent micro-PL to study 

the thermal quenching of individual exciton lines originating from GaInNAs layers grown by 

molecular beam epitaxy. It was observed that the localization energy varies from 0 to 

150meV, whereas the activation energy for each individual line is the same within the 

experimental uncertainty and equals ~6meV [3], see micro-PL spectra for a GaInNAs layer 

together with the determined activation energies in Fig. 1. This observation means that the 

main source of sharp lines are excitons localized on deep donor- (acceptor-) like states. At 

low temperatures these states are able to attend in the radiative recombination because of 

coulomb attraction between electrons and holes, whereas at higher temperatures they do not 

participate in the radiative recombination but they can still trap carriers which recombine 

nonradiative through these states. In this work we will discuss the origin of deep donor- 

(acceptor-) like states in GaInNAs alloys. 

PL intensity (arb. u.) 

E a (meV) 

60 

40 

20 

0 

10 

5 

P ex. = 2mW 

5K 

8K 

12K 

16K 

20K 

24K 

Localized states 

(exciton emission) 

0 

0.86 0.88 0.90 0.92 0.94 0.96 0.98 

Energy (eV) 

188 

Fig.1 Micro-PL spectra measured at various 

temperatures together with activation 

energies determined for individual PL lines. 

The authors acknowledge support from the 

MNiSW (grant nos. N202 258339 and 

DPN/N125/COST/2009) and the COST 

Action MP0805. 

[1] A.M. Mintairov, et al., Phys. Rev. Lett. 

87, 277401 (2001). 

[2] R. Kudrawiec, et al., Appl. Phys. Lett. 

94, 011907 (2009). 

[3] M. Latkowska, et al., Appl. Phys. Lett. 

98, 131903 (2011).

40th _______________________________________________________________ 


Nitride Based Sensors with Ga- and N-polarity 

Malte Fandrich, Gerd Kunert, Timo Aschenbrenner, Stephan Figge, Carsten 

Kruse, and Detlef Hommel 

Universität Bremen – Institut für Festkörperphysik, Otto-Hahn-Allee 1, 28359 Bremen, 

Germany 

Group-III nitrides have emerged as an advantageous material system for various chemical 

and biochemical sensing applications. Material specific properties like their chemical stability 

and large bandgap energies allow high temperature operation even in harsh environments. 

The large spontaneous and piezoelectric polarization along the polar c-direction in nitride 

based heterostructures originates a surface near two-dimensional electron gas (2DEG) 

with a high sheet carrier density. Hence, these structures are highly sensitive to interactions 

at the surface affecting the polarization-induced 2DEG. Using the 2DEG as a 

conductive channel between applied source- and drain-contacts, a manipulation of surface 

charges at the uncoated semiconductor surface causes a change in source-drain current, 

whereby for example polar liquids and gases can be detected. 

In order to investigate the influence of different polarity, GaN-buffer layers were grown on 

sapphire (Al2O3) using both metal-organic vapor-phase epitaxy (MOVPE) and molecularbeam 

epitaxy (MBE). Thus, Ga- (by MOVPE) and N-polar (by MBE) templates were 

obtained, which determine the polarity of subsequently grown layers and consequently the 

complete heterostructures [1]. To increase the sheet carrier density of the heterostructures 

AlGaN layers with different Al-content and Si doping concentration were grown on these 

templates. In addition AlInN/GaN-heterostructures were realized, since Al0.82In0.18N exhibits 

a higher spontaneous polarization than conventionally used Al0.2Ga0.8N [2] and is 

lattice matched to GaN. All epitaxial structures were characterized by high resolution 

X-ray diffraction (HRXRD), atomic force microscopy (AFM) and Hall measurements and 

optimized with respect to their structural and electrical properties. 

Based on the heterostructures open-gate sensors were processed. The sensing behavior of 

these structures was investigated by exposure to polar fluids, where the molecular dipole 

moments in the liquid interact with the polar semiconductor surface [3]. The performances 

of the different devices will be compared and the influence of polarity will be discussed. 

All structures enable the detection and determination of polar liquids by means of a significant 

change in source-drain current. The electrical measurements demonstrated a good 

reproducibility after repeated coverage with the fluids. 

Additionally, the gas detection performance was analyzed by electrical measurements 

under different gas atmospheres, which prove the gas sensing capability of the devices. 

[1] M. Stutzmann, O. Ambacher, M. Eickhoff, U. Karrer, A. Lima Pimenta, R. Neuberger, 

J. Schalwig, R. Dimitrov, P. J. Schuck, and R. D. Grober, phys. stat. sol. (b) 228, 2 

(2001). 

[2] J. Kuzmik, IEEE Electron Device Lett. 22, 11 (2001). 

[3] M. Eickhoff, R. Neuberger, G. Steinhoff, O. Ambacher, G. Müller, and M. Stutzmann, 

phys. stat. sol. (b) 228, 2 (2001). 

189

WeP14 _______________________________________________________________ 


Zinc vacancy induced ferromagnetic interaction in semimagnetic 

semiconductor (Zn,Mn)Te 

Le Van Khoi 1 , K. Swi tek 1 , M. Pawlowski 2 and R. R. Gał zka 1 

1 Institute of Physics, Polish Academy of Sciences. Al. Lotników 32/46, Warsaw, Poland. 

2 Institute of Electronic Materials Technology, ul. Wólczy ska 133, Warsaw, Poland. 

Ferromagnetic (FM) semiconductors are the subject of an intense research activity due 

to their potential applications in spintronics. The basic mechanism that governs 

ferromagnetism in the FM semiconductors is believed to be the carrier-mediated FM coupling 

among the Mn 2+ ions. The carriers are the holes reside in the valence or impurity bands. In 

this communication, we report on experimental evidence of the zinc vacancy mediated FM 

interaction in the (Zn,Mn)Te alloy. We have measured photoluminescence (PL) and electron 

paramagnetic resonance (EPR) on the undoped (Zn,Mn)Te crystals. We have observed a 

strong exchange interaction between the Mn 2+ ions and both the 

0 

− 

neutral donor ( D ) and single charged zinc vacancy ( V Zn ). That 

results in an exchange (Dexter) energy transfer channel from the 

−− 

recombinating donor-deep acceptor ( 

V Zn ) pairs to the Mn 2+ ions 

at T 50 K. The EPR measurements on the annealed samples 

revealed positive Curie-Weiss temperature TCW indicating the 

presence of the FM coupling among the Mn 2+ ions. 

The undoped (Zn,Mn)Te crystals were grown by high 

pressure Bridgman method and annealed under a high pressure of 

N2 gas. The PL measurements show that introduction of Mn into 

the ZnTe host results in a new 1.95 eV PL band originated from 

the intra-3d-shell transitions of the Mn 2+ ions. It was found that 

with the increasing Mn content the Mn emission intensity also 

0 − + −− 

increases, whereas the emission resulted from the D + VZn 

→ D + VZn 

+ hν 

deep transition is 

quenched, and the emission resulted from the 

0 0 + − 

D + VZn 

→ D + VZn 

+ hν 

shall transition 

remains unchanged. This indicates that Mn 2+ ions strongly interact with the paramagnetic D 0 

and V centers via the s,p-d exchange. As a result, an exchange energy transfer channel from 

− 

Zn 

the recombinating 

−− 

D −VZn 0 

pairs to the Mn 2+ ions is triggered. Further, the annealing of the 

(Zn,Mn)Te crystals increases the − 

VZn density and suppresses the compositional fluctuation in 

this material. The effect of 

− 

VZn on the magnetic state of Mn 2+ in (Zn,Mn)Te was studied by 

performing the EPR measurements. We found that after the annealing, the shape of EPR 

spectrum exhibits a homogeneous broadening at T 10 K and its amplitude increases by a 

factor of ~4 (see fig. (a)). The T-dependence of the inverse EPR intensity (1/IEPR) is shown in 

−− 

figure (b). At T 50 K, major of the zinc vacancies are doubly charged ionized ( V Zn ), hence 

only the d-d superexchange interaction via the Te ions dominate and it is characterized by TCW 

~ −225 K. Bellow 50 K, the single ionized zinc vacancies V appear due to the localization 

of holes. The exchange interaction between the hole trapped at the 

− 

Zn 

3000 3200 3400 3600 

Magnetic field (Oe) 

− 

V Zn site and the Mn 2+ ions 

gives rise to the formation of the bound magnetic polarons (BMP). In the annealed sample 

there is a coalescence of BMP. As a result, the FM exchange contribution overcompensates 

the antiferromagnetic d-d superexchange. This makes the T-dependence of 1/IEPR to change its 

curvature at T 50 K and results in TCW ~ +2 K as shown in figure (b) and its inset. 

190 

10 8 / intensity (arb. u.) 

EPR signal (arb. u.) 

2.5 

2.0 

1.5 

1.0 

0.5 

(Zn,Mn)Te 

x=0.03 

x=0.001 

T=5.0 K 

2.5 K 

4.0 K 

5.6 K 

10 K 

As-grown Annealed 

(Zn,Mn)Te 

x=0.03 

T CW = -225 K 

10 9 / Intensity (arb. u.) 

(Zn,Mn)Te 

2.5 

x=0.03 

2.0 

As-grown 

1.5 

1.0 

0.5 

(a) 

(b) 

Annealed 

x=0.07 

Annealed 

0.0 

0 2 4 6 

T (K) 

8 10 12 

0.0 

0 50 100 150 200 250 

Temperature (K)

40th _______________________________________________________________ 


Magnetic Properties of (Ga,Mn)As near Metal-Isolator Transition 

S. Dobkowska 1 , W. Stefanowicz 1 , O. Proselkov 1 , R. Żuberek 1 , J. Sadowski 2 , 

T. Dietl 1,3 , and M. Sawicki 1 

1 Institute of Physics, Polish Academy of Science, Warsaw, Poland 

2 MAX-Lab, Lund University, Lund, Sweden 

3 Institute of Theoretical Physics, University of Warsaw, Warsaw, Poland 

Diluted magnetic semiconductors, especially (Ga,Mn)As, have been intensively 

studied for last decade since they bridge the physics of semiconductors and magnetism. As the 

ferromagnetic (FM) coupling among localized moments (solely Mn so far) is mediated by 

mobile carriers (holes) which concentration is limited either by the presence of Mn itself 

and/or by self-compensating defects in the host material, these materials are frequently found 

to be on the verge of localization of the electronic states. This can be regarded as detrimental 

for wide ranging spintronics applications, but on the other hand such materials serve as a 

powerful tool to study an interplay between magnetism and localization, or even to 

quantitatively investigate the very nature of the metal-insulator transition (MIT). In 

particular, due to qualitatively different magnetic signatures of regions with significantly 

different carrier density, an opportunity is given to trace the evolution of the character of the 

electronic states on crossing the MIT by using direct magnetometry. Therefore we expect to 

find (i) a long range FM order in metallic samples, (ii) percolating or not FM “bubbles” in 

weakly localizes materials, and (iii) uncoupled paramagnetic moments in purely insulating 

samples. But in practice various degrees of combinations of the above contributions are seen, 

so a firm ability of recognizing of these responses in (Ga,Mn)As is required if one wants to 

investigate the transition region. 

The complications start already in ultrathin metallic samples which show considerable 

deviations from the typical for (Ga,Mn)As behavior, as it is shown by Proselkov, et al. [1]. As 

one of the few possible explanation invokes a presence of sizable number of small FM 

volumes (the “bubbles”) created in the near-to-surface depletion zone [2] we perform a 

detailed and a wide-ranging magnetic studies of samples where magnetic response 

characteristic to the metallic phase is very small, or is even completely quenched. For this 

purpose we select a 600 nm thick layer with only 2% of Mn in which the proximity to MIT is 

solely assured by the low Mn concentration. Also, in order to link our findings with those of 

[1] we investigate 5 and 7.5 % layers with thickness ranging from 4 to 8 nm. We perform both 

DC and AC SQUID magnetometry and an angle dependent FMR. All studied samples show a 

coexistence of a temperature reversible magnetization characteristic for a long-range-coupled 

magnetization as well as an irreversible one possessing characteristics similar to a blocked 

superparamagnet. The relative contribution of former to the latter scales down linearly with 

the inverse of the TC of the layer, confirming a gradual localization of the extended states 

already on the metallic side of MIT. The reach T-dependent AC magnetization compares well 

to the DC m(H) studies confirming a presence of both blocked superparamagnetic moment 

and a spin reorientation transition between uniaxial and biaxial magnetic anisotropy in the 

metallic part of the sample. 

The work was supported by EU FunDMS Advanced Grant of the European Research 

Council within the “Ideas” 7 th Framework Programme, EC Network SemiSpinNet (PITN-GA- 

2008-215368) and Polish MNiSW No. 2048/B/H03/2008/34 grant. 

[1] O. Proselkov, W. Stefanowicz, S. Dobkowska, J. Sadowski, T. Dietl, M. Sawicki, 

this conference. 

[2] M. Sawicki, et al., Nature Physics 6, 22 (2010). 

191

WeP16 _______________________________________________________________ 


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192

40th _______________________________________________________________ 


Wide range wavelength tuning of InGaAsP/InP laser diodes 

M. Bajda 1, 2 , F. Dybała 2 , A. Bercha 2 , W. Trzeciakowski 2 , and J. A. Majewski 1 

1 Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, Poland 

2 Institute of High Pressure Physics Unipress, Polish Academy of Sciences, Poland 

The combination of pressure and temperature tuning with external-grating tuning [1] has 

been studied both theoretically and experimentally [2]. Bent-waveguide InGaAsP/InP laser 

diode (manufactured by Covega [3]) is tuned under pressure up to 2.2 GPa in the external 

cavity formed by diffraction grating. Due to bent waveguide, there is no reflection at the laser 

facet, independently of wavelength or the medium in which the laser is immersed. At each 

pressure the laser is tuned by the grating in the 60-120 nm range. The total tuning range that 

can be achieved with pressure and grating amounts to 390 nm (from 1610 nm down to 1220 

nm). Temperature tuning (in the 300K-100K range) has turned out to be less effective, mostly 

because of the strong tuning range reduction at low temperatures. 

In order to model the experimental results, 

we have performed calculations of gain as 

a function of pressure and temperature, 

employing an 8x8 k·p scheme [4] for electronic 

structure of the InGaAsP quantum well. The gain 

has been obtained as a function of carrier 

concentration and the concentration, in turn, has 

been related to current assuming two 

recombination channels: radiative and Auger 

ones. Since the radiative recombination 

dominates in temperatures up to 250K, 

Fig.1 Bent waveguide chip with highly 

reflective back mirror and anti-reflective 

coating on the front mirror. 

knowledge of the temperature dependence of the threshold currents allows for separation of 

these two contributions. At each pressure/temperature we are able to calculate the threshold 

currents as a function of wavelength by requiring that the modal gain equals the total losses 

(mirror losses and the internal optical losses). We obtain fairly good agreement between the 

theory and experiment. This opens new perspectives of possible future developments of this 

new method for wave-length tuning of laser diodes. 

[1] C. Ye, Tunable external cavity diode lasers (World Scientific, Singapore, 2004). 

[2] F. Dybala, A. Bercha, P. Adamiec, R. Bohdan, and W. Trzeciakowski, Phys. Status Solidi 

B 244, 219 (2007). 

[3] http://www.covega.com/Products/pdfs/SAF%201126%20Rev%20C.pdf 


193

WeP18 _______________________________________________________________ 


Transport properties of GaMnAs layers 

M. Gryglas-Borysiewicz 1 , J. Przybytek 1 , M. Baj 1 , A. Kwiatkowski 1 , P. Juszy�ski 1 , 

D. Wasik 1 , P. Dziawa 2 and J. Sadowski 2,3 

1 Faculty of Physics, University of Warsaw, Ho�a 69, 00-681 Warsaw, Poland 


3 Max-Lab, Lund University, Lund, SE-221 00, Sweden 

(Ga, Mn)As is one of the most intensively investigated diluted magnetic semiconductors 

during last decades. The understanding of physical phenomena governing its magnetic 

properties is crucial for possible application of this material in spintronic devices. One of the 

issues that are currently addressed is the interplay between carrier localization and magnetic 

properties of the layers [1-3]. It was observed that for insulating sample a decrease of the 

interatomic distances leads to a decrease of the Curie temperature, in contrast to metallic 

sample, for which the Curie temperature was increased [3]. 

In order to extend the studies presented in [3] a series of new samples was prepared. 

50nm-thick Ga1�xMnxAs layers were grown by molecular-beam epitaxy on (100) GaAs semiinsulating 

substrates. Three kinds of samples were studied: two with x = 2% and different 

compensations and one with x = 6%. The two former samples had Curie temperature TC about 

20 K and the latter one – 70 K. Standard Hall bars were prepared by means of optical 

lithography and six ohmic contacts were made with indium. The samples were investigated 

using magnetotransport measurements down to 4K, with magnetic field up to 7T. 

Figure 1 shows the temperature variation of resistivity. As planned, the samples 

have qualitatively different character: from metallic (lower curve) to highly insulating (top 

curve) one. The Hall and longitudinal voltages were measured as a function of magnetic field. 

The evolution of hysteresis observed in both �xx(B) and �xy(B) will be used to determine the 

Curie temperature and thus to analyze the localization of holes in the samples within the 

generalized alloy theory [1]. 

� (cm *�) 

10 

1 

0.1 

10 20 30 40 50 60 70 80 90 100 110 

T (K) 

Figure 1. Resistivity of the studied samples as a function of temperature. 

[1] T. Dietl, Phys. Rev. B 77, 085208 (2008). 

[2] M. Sawicki et al., Nature Physics 6, 22 (2010) 

[3] M. Gryglas-Borysiewicz et al., Phys. Rev. B 82, 153204 (2010) 

194 

�

40th _______________________________________________________________ 


Group III-nitrides growth on N-polar substrates 

C. Chèze 1 , M. Sawicka 1,2 , M. Siekacz 1,2 , H. Turski 2 , A. Feduniewicz-Zmuda 2 , 

G. Cywiński 2 , B. Grzywacz 2 , S. Grzanka 2 , I. Dziecielewski 2 , B. ̷Lucznik 1,2 , M. 

Boćkowski 1,2 , and C. Skierbiszewski 1,2 

1 TopGaN Ltd, Soko̷lowska 29/37, 01-142 Warszawa, Poland 

2 Institute of High Pressure Physics, PAS, Soko̷lowska 29/37, 01-142 Warszawa, Poland 

Thegrowthofnitrogen-polar(N-polar)groupIII-nitridesbyplasma-assistedmolecular 

beam epitaxy (PAMBE) is currently raising a lot of interest. One of the advantages of 

the growth along the [000¯1] over the [0001] direction is the highest thermal dissociation 

limit of N-face InGaN allowing for a more efficient In incorporation in N-face InGaN 

[1]. Another benefit of the growth along the [000¯1] direction lies in the formation of 

polarization-induced three dimensional hole gas at the interface of N-polar GaN-AlGaN 

with graded Al content. This method proposed by Simon et al [2] proves very efficient 

p-type doping. However, N-face III-nitrides (000¯1) usually suffer from poor morphology 

as no Ga bilayer can be stabilized at the growth front [3]. Therefore a new growth window 

under N-rich conditions as has been found for the Ga-face (0001) [4] and m-plane (10¯10) 

[5] would be highly desirable. 

In this work we study the growth of GaN, InGaN and AlGaN-GaN quantum wells 

on N-polar (000¯1) GaN by PAMBE. Similarly to the growth of nitrides on Ga-polar 

face (0001), we have achieved high quality step-flow growth of GaN on N-polar in the 

metal-rich regime. The surface of this layer is extremely smooth and we clearly observe 

single atomic steps flowing towards the [10¯10] direction when every second step edge is 

either straight or jagged. For Ga-polar GaN, a similar surface morphology was observed 

and explained by the growth anisotropy of two alternating types of step-edges [6]. In 

addition, the photoluminescence (PL) spectra at room temperature of the N-polar GaN 

layer exhibit a sharp peak at 363 nm with a full width at half maximum value of 4.53 

nm. In contrast, the N-rich regime results in a defect-mediated growth morphology, where 

stripes nevertheless covered by atomic steps meander between depressions and hillocks. 

We will discuss the effect of the III/V ratio on the growth mode of N-polar GaN. We will 

also compare the growth and characteristics of InGaN and AlGaN-GaN quantum wells 

grown in the metal-rich regime on N- and Ga-polar substrates. These preliminary results 

open up new possibilities for more efficient N-polar based deep ultra-violet and green 

optoelectronic applications. 

[1] J. Simon, V. Protasenko, C. Lian, H. Xing, and D. Jena, Science 327, 60 (2010) 

[2] D. N. Nath, E. Gr, S. A. Ringel, and S. Rajan, Appl. Phys. Lett. 97, 071903 (2010) 

[3] E. Monroy, E. Sarigiannidou, F. Fossard, N. Gogneau, E. Bellet-Amalric, J. L. Rouviere, 

S. Monnoye, H. Mank, and B. Daudin, App. Phys. Lett. 84, 2684 (2004). 

[4] G. Koblmuller, F. Wu, T. Mates T, J. S. Speck JS, S. Fernandez-Garrido, and E. 

Calleja, App. Phys. Lett. 91, 221905 (2007). 

[5] M. Sawicka, et al., J. Vac. Sci. Technol. B in press (2011). 

[6] M.H. Xie, S.M. Seutter, W.K. Zhu, L.X. Zheng, H. Wu, S.Y. Tong, Phys. Rev. Lett. 

82, 2749 (1999) 

This work was supported partially by the Polish Ministry of Science and Higher Education Grant No 

IT 13426 and the European Union within European Regional Development Fund, through grant Innovative 

Economy (POIG.01.01.02-00-008/08) and within FP7-PEOPLE-IAPP-2008 through grant SINOPLE 

230765. 

195

WeP20 _______________________________________________________________ 


Absorption and Emission Properties of Light Emitting Diode Structures 

Containing GaInN/GaN QWs 

J. Binder 1 , K. P. Korona 1 , J. Borysiuk 1 , M. Kaminska 1 , M. Baeumler 2 , K. Köhler 2 , 

L. Kirste 2 

1 Faculty of Physics, University of Warsaw, ul. Hoza 69, 00-681 Warsaw, Poland 

2 Fraunhofer Institute for Applied Solid State Physics, Tullastr. 72, 79108 Freiburg, Germany 

The technology of illumination is about to change towards an effective, energy saving 

future. A major role in this development is played by light emitting diodes (LEDs) which have 

the advantage of being a very effective and low cost light emitter. Structures based on GaN 

are playing an important role in the field of light emitting devices and a deeper understanding 

of the processes involved in light emission is therefore needed to further increase the 

capability of the produced structures. 

In this work we present measurements of 3 samples that have different quantum well 

(QW) widths (1.8 nm, 2.7 nm, 3.7 nm). The samples were grown on a sapphire substrate with 

a nucleation and a buffer layer of GaN, followed by a n-doped layer of GaN:Si. The active 

layer consists of 3 QWs made of GaN/Ga0.9In0.1N heterostructures followed by an 

AlxGa(1-x)N:Mg barrier (xAl about 0.04) and a p-doped layer of GaN:Mg. All layers were 

produced by MOCVD. Semitransparent Schottky contacts were evaporated on the surface. 

The ohmic contacts were made on the edges to connect the GaN:Si layer. The details of the 

structure were confirmed by high resolution electron microscopy. 

Numerical calculations of the electric field and potential profiles were performed for 

this structure. It has been found that due to the spontaneous polarization and the piezoelectric 

effect a strong electric field of the order of 1 MV/cm (100 mV/nm) was present in the GaInN 

QWs. This field has a reverse direction in comparison to the field generated by the p-n 

junction. 

In order to characterize the sample, measurements of photoluminescence (PL), 

electroluminescence (EL) and photocurrent (PC) were performed at room temperature. The 

emission was measured as a function of applied voltage revealing shifts caused by the 

quantum confined stark effect (QCSE). 

A strong emission of the QWs could be observed in EL at energies 3.07 eV, 3.11 eV and 

3.18 eV, for the QWs of width 3.7 nm, 2.7 nm and 1.8 nm, respectively. An additional peak 

from GaN was visible in PL at 3.4 eV. The different QW widths resulted in different emission 

energies, which can be explained by different quantization energies and the presence of the 

internal electric field caused by spontaneous and piezoelectric polarizations. The photocurrent 

measurements show the presence of spectral bands related to the GaInN QWs, GaN and 

AlGaN. The PC bands correspond strictly to the absorption bands at room temperature due to 

efficient delocalization of photoexcited carriers. The energy thresholds of the QW absorption 

bands decreased with increasing QW width from 3.19 eV for the 1.8 nm-QW to 3.11 eV for 

the 3.7 nm-QW, similarly to the case of emission. 

The comparison of the emission (EL and PL) and absorption (PC) on the same sample 

revealed a shift in energy, with the emission energy being significantly lower. This can be 

interpreted by a shift of the ground state energy caused by the QCSE. The shifts were higher 

for wider QWs, in agreement with even most simple theoretical calculations. More detailed 

numerical calculations were performed for a further study of the structure (taking into account 

the electric field inside and outside the sample). The obtained information is among other 

things helpful for the determination of radiative and nonradiative processes in light emitting 

diodes. 

196

40th _______________________________________________________________ 


Mn contribution to the valence band of Ga1−xMnxSb 

B.J. Kowalski 1 , R. Nietubyć 2 , and J. Sadowski 3,1 


Poland 

2 The Andrzej Soltan Institute for Nuclear Studies, 05-400 Swierk/Otwock, Poland 

3 MAX-lab, Lund University, Box 118, SE-22100 Lund, Sweden 

The contribution of the Mn 3d states to the valence band of Ga1−xMnxSb, an important 

factor determining the properties of this system, has been revealed by photoelectron spectroscopy. 

The resonant photoemission experiment, carried out for photon energies close 

to the Mn 3d → 3p excitation, allowed us to identify the spectral feature corresponding 

to emission from the Mn 3d states. The scanning of the valence band along the [100] and 

[011] directions in the Brillouin zone, made by the angle-resolved photoemission experiment, 

showed that these states contributed to a dispersionless structure at the binding 

energy of 3.5 eV (with respect to the Fermi energy). Other bands were similar to those 

reported for GaSb [1]. 

Ga1−xMnxSb is a III-V diluted magnetic semiconductor exhibiting ferromagnetic properties, 

although at relatively low temperatures (Tc=25 K [2]). It has been investigated 

much less than Ga1−xMnxAs but it attracts interest due to the opportunity to study the 

interactions of magnetic ions with charge carriers in a host with anions chemically different 

than in arsenides or due to the band structure of Ga1−xMnxSb particularly suitable 

for making a novel device (a ferromagnetic resonant interband tunneling diode [3]). 

The photoemission experiments were performed with use of the photoelectron spectrometer 

at the beamline 41 in the MAXlab synchrotron radiation laboratory of Lund 

University (Sweden). The sets of spectra were collected in the normal emission mode for 

the photon energy ranges from 30 to 51 eV (in order to observe the Mn 3p-3d resonance) 

and from 50 to 106 eV (to scan the band structure along the [100] direction) as well as in 

the off-normal mode (to scan the band structure along the [011] direction). 

The Ga1−xMnxSb layers with Mn contents in the range of 1 to 3%, were grown on 

GaSb(100) substrates by molecular beam epitaxy (MBE) at low substrate temperature of 

about 230 o C. The MBE growth was monitored by Reflection High Energy Electron Diffraction 

(RHEED).The 2-dimensional diffraction patterns (streaks) and distinct RHEED oscillations 

were observed throughout the growth of the Ga1−xMnxSb layers up to their 

final thicknesses (50 to 300 ˚A depending on the sample). No signs of secondary phases 

(segregated MnSb nanocrystals [4]) were detected on RHEED images after the growth. 

The (100) surfaces of the layers exhibited the Low Energy Electron Diffraction (LEED) 

patterns corresponding to the asymmetric (1x3) reconstruction. The absence of MnSb 

precipitates in the investigated samples was confirmed also by a comparative study (including 

the samples containing the precipitates) by scanning electron microscopy. 

This research has received funding from the European Community’s Seventh Framework 

Programme (FP7/2007-2013) under grant agreement no. 226716. 

[1] G.E. Franklin, D.H. Rich, A. Samsavar, E.S. Hirschorn, F.M. Leibsle, T. Miller, 

T.-C. Chiang, Phys. Rev. B 41, 12 619 (1990) 

[2] F. Matsukura, E. Abe, H. Ohno, J. Appl. Phys. 87, 6442 (2000) 

[3] I. Vurgaftman, J.R. Meyer, Appl. Phys. Lett. 82, 2296 (2003) 

[4] K. Lawniczak-Jablonska, A. Wolska, M.T. Klepka, S. Kret, J. Gosk, A. Twardowski, 

D. Wasik, A. Kwiatkowski, B. Kurowska, B.J. Kowalski, J. Sadowski, J. Appl. Phys. 

109, 074308 (2011). 

197

WeP22 _______________________________________________________________ 


Time resolved photoluminescence studies for GaInNAsSb quantum wells 

emitting at 1.3 µm 

M. Baranowski 1 , M. Latkowska 1 , M. Syperek 1 , R. Kudrawiec 1 , J. Misiewicz 1 , 

T. Sarmiento 2 , and J.S. Harris 2 , 



2 Solid State and Photonics Laboratory, Stanford University, Stanford, California 94305-4075 

Dilute nitrides (e.g., GaInNAs with a few percent of nitrogen atoms) have attracted much 

attention due to their potential use in low cost telecommunication laser based on GaAs 

operating at II and III telecommunication windows. However with increasing nitrogen mole 

fraction the optical quality of GaInNAs material strongly deteriorates due to point defects, 

nitrogen interstitials, vacancy-type defects as well the phase separation [1]. In the past few 

years it has been found that the introduction of antimony, forming GaInNAsSb alloy, greatly 

improves the optical quality of this material system [1, 2]. This is because of reactive 

surfactant properties of antimony which reduces the group-III surface diffusion length thereby 

suppress the phase segregation in this material system [1]. This improvement is well 

documented by photoluminescence (PL) measurements as well as structural investigations [1]. 

However, so far no time resolved photoluminescence (TRPL) studies on such QWs have been 

reported. In this work we applied TRPL spectroscopy to investigate the phenomenon of 

carrier localization at low temperatures as well as the influence of non-radiative 

recombination on the efficiency of PL emission from the as-grown and annealed GaInNAsSb 

QWs. 7nm-wide Ga0.68In0.32N0.02As0.96Sb0.02/GaAs QWs were grown by molecular beam 

epitaxy and annealed at different temperatures varying from 680 to 800 °C. TRPL 

measurements were performed for different excitation powers and the spectra were measured 

at various temperatures. Some dispersions of PL decay time, which are related to carrier 

localization phenomenon, were observed at low temperatures but they disappear very quickly 

just above 40 K. In order to evaluate the contribution of non-radiative recombination, the PL 

decay time was measured at room temperature and compared for the as-grown and annealed 

samples. It was observed that the longest PL decay time (i.e., the best sample quality) is 

observed for samples annealed at ~720 °C. This time equals ~700 ps whereas for the as-grown 

sample this time equals ~100 ps. The measured PL decay times are the longest which were 

observed for this material system (dilute nitrides QWs) so far. This is an evidence of the high 

quality of GaInNAsSb QWs. In this work physical mechanisms, which are responsible for 

changes in the dynamic of photoluminescence as well as the origin of optical quality 

improvement upon annealing, will be discussed. 

The authors acknowledge support from the MNiSW (grant no. N202 258339). 

[1] J.S. Harris, et al., Physica Status Solidi (b) 244, 2707 (2007), and references therein. 

[2] X. Yang, et al., Appl. Phys. Lett. 75, 178 (1999). 

198

40th _______________________________________________________________ 


InGaN laser diodes with passive absorber section. 

A. Kafar, J. Goss, S. Stańczyk, R. Czernecki, M. Leszczynski, T. Suski, P. Wiśniewski, 

P . Perlin 

Institute of High Pressure Physics “Unipress”, Sokolowska 29/37, 01-142 Warsaw, Poland 

The laser diode cavities with the passive (non-injected) section form interesting system 

because of its possibility to generate self-pulsation via passive Q-switching effect. In this 

work we present the properties of two segmented laser diodes in which one section may 

remain unbiased (or negatively biased) during the operation. Such a system is thought to be 

useful as simple realization of the superluminescent diodes (SLEDs) since high absorption of 

the passive segment prevents the system for lasing in the low-medium currents range. As a 

result such a SLED can demonstrate the optical powers ranging up to few miliwats. However, 

even high losses do not prevent system from lasing under high current regime. The lasing 

starts when the gain overcomes high cavity losses. By using Hakki-Paoli method we 

measured the gain and determined the losses of the passive part of the resonator. In the final 

part of this work we discuss: i) the properties of the system within the saturable absorber 

model and ii) possible applications for the realization of picoseconds lasers and 

superluminescent diodes. 

Figure 1. Optical power versus current curve showing superluminescent and lasing regimes. 

To the right a microphotograph of the two segment device. 

199

WeP24 _______________________________________________________________ 


Evidence of a new magnetic order in short-period (Ga,Mn)As/GaAs SLs 

W. Szuszkiewicz 1* , F. Ott 2 , J.Z. Domagała 1 , E. Dynowska 1 , J. Sadowski 1,3 

1 Institute of Physics PAS, Al. Lotników 32/46, Warsaw, Poland 

2 CEA/CNRS IRAMIS, LaboratoireLéon Brillouin, CE Saclay, 91191 Gif-sur-Yvette, France 

3 MAX-Lab, Lund University, SE-22100, Lund, Sweden 

Short-period (Ga,Mn)As/GaAs superlattices (SLs) containing about 5% of Mn in 

(Ga,Mn)As layer were grown in a MBE system (KRYOVAK) equipped with an As2 valve 

cracker source. The number of repetitions was 100. The low-temperature growth of structures, 

performed at 200°C was preceded by a standard high-temperature growth of a 5000 thick 

GaAs buffer, deposited onto semi-insulating, (100)-oriented GaAs wafers. The Mn 

composition in (Ga,Mn)As layers was determined from the analysis of RHEED intensity 

oscillations during the growth. The structure quality of the SLs was checked by X-ray 

diffraction measurements using the high-resolution Philips diffractometer and Cu Kα1 

radiation. Magnetic properties of (Ga,Mn)As/GaAs SLs were characterized by means of 

magnetization measurements using a SQUID, the TC values estimated on the basis of these 

measurements ranged from 30 K to 50 K. 

The samples were investigated by polarized neutron reflectometry on the spectrometer 

PRISM at the LLB. The presence of a ferromagnetic-like exchange interlayer coupling 

between the (Ga,Mn)As layers, observed long time ago for both long-period [1] and shortperiod 

[2] SLs was confirmed. Due to the lack of intentional, high p-type doping, no trace of 

the interlayer coupling of antiferromagnetic type was detected (such coupling has been 

recently reported for SLs with Be-doped GaAs spacers [3]). Apart from the expected 

ferromagnetic order in the system under investigations the neutron spectra demonstrated a 

presence of a supplementary, incommensurate magnetic order, which takes place at low 

temperature (10K) and low magnetic fields (

40th _______________________________________________________________ 


Application of n-GaN layers grown by MBE for light- induced water 

splitting and hydrogen generation 

Z. Wiśniewski 1 , K. Izdebska 1 , P. Sybilski 1 , Z. R. Żytkiewicz 1 , M. Sobańska 1 , K. 

Kłosek 1 , A. Reszka 1 , B. J. Kowalski 1 , A. Suchocki 1,2 

1 Institute of Physics Polish Academy of Science Al. Lotników 32/46 02-668 Warsaw, Poland 

2 Institute of Physics, University of Bydgoszcz, Weyssenhoffa 11, 85-072 Bydgoszcz Poland 

GaN is a very promising material for environment friendly photovoltaic applications, 

especially for a hydrogen generation. Hydrogen is generated by photo – catalytic water 

decomposition carried out in electrochemical cells with one electrode made of semiconductor 

is exposed to the light and the second one made of metal. Electrical connection is provided by 

aqueous electrolyte which is simultaneously the source of the water. For practical application 

of this process, a semiconductor must satisfy the following conditions [1]: (i) a band-gap 

energy must be at least 1.7 – 1.9 eV, (ii) redox potential for water reduction must be below the 

conduction band energy and the water oxygenation redox potential must be above the valence 

band energy; (iii) the semiconductor must have high resistance to corrosion and photocorrosion 

processes. In order to satisfy the condition (ii) often it is necessary to apply external 

voltage. GaN-based materials can fulfill all of above requirements. The aim of this work was 

to check the influence of electrolyte on efficiency of water splitting reaction and hydrogen 

generation in photocells with n type-GaN. 

1 m thick n-GaN layers were grown on Si(111) substrates by plasma-assisted MBE 

technique. The morphology of GaN surfaces was investigated by SEM technique. They were 

used as photo-anodes in specially designed photocells. A counter electrode was made of 

platinum. In this way the electrochemical chain n-GaN/electrolyte/ platinum was obtained. 

Na2SO4, NaCl, and KOH solutions of different concentrations were used as electrolytes. The 

n-GaN plates were illuminated by white light and by a He-Cd laser beam of 325 nm 

wavelength. 

Under the irradiation of UV beam and with presence of additional voltage water 

decomposition takes place, which is seen as hydrogen and oxygen bubbles formed on the 

surfaces of electrodes. The value of external bias needed for water decomposition decreases 

with a concentration of electrolyte. In the case of Na2SO4 required biases decrease from 1.4 V 

for 0.1 mol solution to 0.9 V for 0.5 mol solution. For NaCl solution required external bias is 

higher. I(V) characteristics of n-GaN/electrolyte/platinum systems were measured as a 

function of the intensity of light and electrolyte. We have also found that observed current 

intensity decreases with time due to the photo-corrosion of n-GaN, which might be related to 

high dislocation density commonly observed in GaN on Si structures. The effect of photocorrosion 

on the surface of n-GaN samples was studied with use of optical spectroscopy 

methods and by SEM. Design of special protective layers to reduce degradation effects in 

progress. 

Acknowledgment This work was partly supported by the European Union within European 

Regional Development Fund, through the Innovative Economy Grants (POIG. 01.01.02-00- 

108/2009/2 and POIG. 01.03.01-00-159/08) 

[1] T. Bak, J. Nowotny, M. Rekas, and C.C. Sorrel , Int. Jour. of Hyd. Energy. 27, 991 (2005). 

201

WeP26 _______________________________________________________________ 


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0) 1 3 

9 : 0) 

!1 4$ 9 : 

& ( 0) / 

0) ! 1 2$ 

0) 

& ! $ 

5 1 " + 

!51"+$ 1 2 . ! )*+$ 

1 3 4 )*+ ; 

40th _______________________________________________________________ 


Microwave techniques investigations of (Zn,Co)O films grown by Atomic 

Layer Deposition 

M.I. Łukasiewicz 1 , A. Cabaj 2 , M. Godlewski 1,2 , E. Guziewicz 1 , A. Wittlin 1 , 

M. Jaworski 1 , A. Woło 1 , Z. Wilamowski 1 

1 Institute of Physics PAS, Al. Lotników 32/46, 02-668 Warsaw, Poland 

2 Dept. Mathematics and Natural Sciences College of Sciences UKSW, Dewajtis 5, 


Atomic Layer Deposition (ALD)-grown (Zn,Co)O films are studied in the present work. ALD 

technique enables us to control film uniformity of (Zn,Co)O, as demonstrated recently [1]. 

The (Zn,Co)O films were grown at low temperature (the growth temperature < 300°C). 

Magnetic properties of these films are discussed in [1,2]. Magnetic investigations indicate that 

room temperature ferromagnetic (FM) response is observed in films with non-uniform Co 

distribution only [2]. The observed FM response is due to Co metal accumulations at the 

(Zn,Co)O/Si interface [2]. (Zn,Co)O films with the uniform Co distribution remain 

paramagnetic even at increased concentration of Co and intrinsic defects. 

In the present work we determine an inter-link between uniformity of Co distribution and 

electrical and magnetic response of the films. We employed two microwave techniques for 

these studies. 

The first is microwave AC conductivity. The microwave conductivity method is highly 

sensitive to detect small inclusions with high conductivity. Moreover, this is contactless 

method. Thus, we avoid problems with contact stability and measurements of highly resistive 

samples. Therefore, AC measurements allow us to investigate uniformity of Co-distribution in 

(Zn,Co)O films, since the presence of metal inclusions results in large deviations between DC 

and AC conductivity. Whereas the DC conductivity of our (Zn,Co)O films varies little among 

all studied samples, the AC one increases considerably for the layers with a substantial nonuniform 

Co-distribution and so strongly indicating an important, if not a dominant role of 

metallic inclusions. We demonstrate direct correlation between sample uniformity, magnetic 

response and AC conductivity of our films. 

The second is electron spin resonance technique. These investigations were performed for the 

films with different Co fractions and different uniformity of Co distribution. They allow us to 

observe FM response at low temperature and determine magnitude of anisotropy fields, 

suggesting occurrence of magnetic order even in strongly diluted (Zn,Co)O samples. 

The research was partially supported by the EU within the European Regional Development 

Fund through grant Innovative Economy (POIG.01.01.02-00-008/08) and FunDMS Advanced 

Grant within the "Ideas" 7th Framework Programme of the EC. 

[1] M. Łukasiewicz et al., Acta Physica Polonica (A) (in press) 

[2] M. Godlewski et al., Phys. Status Solidi (b) (in press). 

203

WeP28 _______________________________________________________________ 


Band-structure analysis from photoreflectance spectroscopy in (Ga,Mn)As 

O. Yastrubchak 1 , T. Andrearczyk 2 , J. Sadowski 2,3 , J. uk 1 and T. Wosi ski 2 

1 Institute of Physics, UMCS, Pl. M. Curie-Skłodowskiej 1, 20-031 Lublin, Poland 

2 Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa, Poland 

3 MAX-Lab, Lund University, 22100 Lund, Sweden 

The ternary III-V semiconductor (Ga,Mn)As has recently drawn a lot of attention as the 

model diluted ferromagnetic semiconductor, combining semiconducting properties with 

magnetism. Intentionally undoped (Ga,Mn)As layers, grown by the low-temperature 

molecular-beam epitaxy (LT-MBE) technique, are p-type, where Mn atoms, substituting Ga 

atoms in the GaAs crystal lattice, supply both itinerant holes and magnetic moments. Below a 

magnetic transition temperature, TC, substitutional Mn 2+ ions are ferromagnetically ordered 

owing to interaction with spin-polarized holes. However, the character of electronic states 

near the Fermi energy and the valence-band structure in ferromagnetic (Ga,Mn)As are still a 

matter of controversy. There are two alternative models of the band structure in (Ga,Mn)As. 

The first one assumes mobile holes residing in the valence band of GaAs and the Fermi level 

position determined by the concentration of valence-band holes. The second one involves 

persistence of the narrow, Mn-related, impurity band in highly Mn-doped (Ga,Mn)As with 

metallic conduction. In this model the Fermi level exists in the impurity band within the band 

gap and the mobile holes retain the impurity band character. 

In this paper we have applied photoreflectance (PR) spectroscopy to study the bandstructure 

evolution in (Ga,Mn)As layers with increasing Mn content. Magnetic properties of 

the layers were characterized with SQUID magnetometery. We investigated thick (230 – 300 

nm) (Ga,Mn)As layers with Mn content in the range from 1% to 6% and, as a reference, 

undoped GaAs layer, grown by LT-MBE on semi-insulating GaAs substrates. In addition, we 

investigated two thin (50 nm) (Ga,Mn)As layers (quantum wells) embedded in LT-GaAs. 

Importantly, the (Ga,Mn)As quantum wells displayed significantly higher TC with respect to 

that of thick (Ga,Mn)As layers of the same Mn content. 

The PR spectra measured in the photon-energy range from 1.3 to 1.7 eV revealed a rich, 

modulated structure containing peaks around the band-gap-transition energy and electricfield-induced 

Franz-Keldysh oscillations (FKO) at energies above the fundamental absorption 

edge. From analysis of the FKO periods we obtained the interband transition energies in 

(Ga,Mn)As layers with various Mn contents. In (Ga,Mn)As with a low (1% and 2%) Mn 

content this energy was slightly blue shifted with respect to that in the reference LT-GaAs 

layer, which was interpreted as a result of the Moss-Burstein shift of the absorption edge due 

to the Fermi level location below the top of GaAs valence band. On the other hand, a 

substantial red shift of the transition energy, revealed in (Ga,Mn)As with higher (4% and 6%) 

Mn content, was interpreted in terms of a disordered valence band, extended within the band 

gap, formed in highly Mn-doped (Ga,Mn)As from merging the Mn-related impurity band with 

the host GaAs valence band. These findings are consistent with our recent results obtained 

from the full-line-shape analysis of the PR spectra [1]. 

O. Y. acknowledges financial support by the Foundation for Polish Science under Grant 

POMOST/2010-2/12. This work was also supported by the Polish Ministry of Science and 

Higher Education under Grant No. N N202 129339. 

[1] O. Yastrubchak, J. uk, H. Krzy anowska, J.Z. Domagała, T. Andrearczyk, J. Sadowski, 

T. Wosi ski, arXiv:1012.4760 (Phys. Rev. B, accepted) 

204

40th _______________________________________________________________ 


Influence of Nitrogen Plasma Parameters on Growth of GaN by Plasmaassisted 

Molecular Beam Epitaxy 

K. Klosek, M. Sobanska, Z.R. Zytkiewicz, H. Teisseyre, E. Lusakowska, 

A. Wierzbicka, P. Nowakowski, and L. Klopotowski 

Institute of Physics, Polish Academy of Science, Al. Lotnikow 32/46, 02 668 Warsaw, Poland 

It is already well known that the best GaN layers obtained by plasma-assisted molecular 

beam epitaxy (PAMBE) are grown under Ga-rich conditions with a bilayer of gallium present 

on the surface. Since under such conditions the growth is limited by flux of active nitrogen 

fine tuning of nitrogen source must be used for precise growth. The aim of this work is to 

study how to control parameters of RF nitrogen plasma cell and what is their influence on 

properties of GaN layers. 

GaN layers were grown at temperature of 720 o C on commercially available 

GaN/sapphire templates using Riber Compact 21 system equipped with elemental sources of 

Al, Ga, In, Si, and Mg. Active nitrogen was supplied from an Addon RF plasma source. An 

optical Si sensor was used to measure the light intensity emitted by the nitrogen source in the 

wavelength range of 750 to 850 nm. The sensor converts light emitted by the plasma into 

output voltage U. 

nitrogen flow [sccm] 

7 

6 

5 

4 

3 

2 

1 

U = 1.5 V 

U = 1.8 V 

U = 2.0 V 

U = 2.2 V 

U = 2.4 V 

U = 2.6 V 

300 350 400 450 500 550 600 

RF power [W] 

Fig.1: RF power and nitrogen flow 

values for a fixed sensor output U. 

growth rate [nm/min] 

5,5 

5,0 

4,5 

4,0 

3,5 

3,0 

2,5 

U = 1.5 V 

2,0 

1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 

nitrogen flow [sccm] 

Fig. 2: GaN growth rate vs. nitrogen 

flow for U=1.5 V and U=2.4 V. 

1,4 1,5 1,6 1,7 1,8 1,9 2,0 2,1 2,2 2,3 2,4 2,5 2,6 2,7 

sensor output signal U [V] 

Fig. 3: GaN growth rate vs. sensor 

signal U for nitrogen flow of 2.5 sccm. 

Nitrogen plasma intensity, and so the optical sensor output voltage U, depends both on 

the RF power and the nitrogen gas flow. This is illustrated in Fig. 1 that shows broad range of 

RF power and nitrogen flow parameters giving fixed value of sensor output U. In Fig. 2 the 

GaN growth rate vs. nitrogen flow is plotted for U=1.5 V and U=2.4 V. For each point the 

gallium flux was adjusted to keep the surface covered by 2ML of Ga. As seen, the growth rate 

does not change when the plasma parameters vary along the red (U=1.5 V) and the orange 

(U=2.4 V) curves in Fig. 1. On the contrary, the growth rate monotonically increases with 

intensity of light emitted by nitrogen plasma as shown in Fig. 3. Since under gallium-rich 

conditions growth is controlled by nitrogen flux, results shown in Figs. 2-3 clearly indicate 

that the optical sensor output signal is a direct measure of the amount of active nitrogen 

species available for growth. 

Optical spectra of the plasma were measured to check how intensity of light emitted by 

atomic and molecular nitrogen species depend on nitrogen flow and RF power of the cell. 

Finally, 0.7 µm thick GaN layers were grown under Ga-rich conditions with various nitrogen 

cell parameters to study if their properties, as seen by AFM, XRD, low temperature PL, and 

by electrical measurements, depend on the RF power and/or the nitrogen flow used during 

growth. 

This work was supported by the European Union within European Regional Development 

Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08 NanoBiom). 

U = 2.4 V 

205 

growth rate [nm/min] 

6,5 

6,0 

5,5 

5,0 

4,5 

4,0 

3,5 

3,0 

2,5 

N 2 flow = 2.5 sccm

WeP30 _______________________________________________________________ 


Deep defects in ZnO/GaN heterostructure analyzed by the admittance 

spectroscopy 

T. A. Krajewski 1 , P. Stallinga 2 , E. Zielony 3 , P. Kruszewski 1 , K. Go ci ski 1 , 

Ł. Wachnicki 1 , S. Figge 4 , D. Hommel 4 , E. Guziewicz 1 1, 5 

, M. Godlewski 

1 Institute of Physics, Polish Acad. of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland 

2 Universidade do Algarve, Campus de Gambelas, FCT, 8005-139 Faro, Portugal 

3 Institute of Physics, Wroclaw University of Technology, 

Wybrze e Wyspia skiego 27, 50-370 Wrocław, Poland 

4 University of Bremen, Institute of Solid State Physics, 

Kufsteiner Strasse 1, Bremen 28359, Germany 

5 Dept. of Mathematics and Natural Sciences College of Science 

Cardinal S. Wyszy ski University, ul. Dewajtis 5, 01-815 Warsaw, Poland 

Zinc oxide (ZnO) is currently widely investigated as a very promising II-VI 

semiconducting material for various electronic and optoelectronic purposes. For many of its 

modern applications it is useful to understand the physics behind the electrical properties of 

this compound. This is strongly related to the knowledge of shallow and deep defect levels of 

ZnO [1, 2]. 

In this work an Ag/ZnO/GaN/Au device was analyzed with the admittance 

spectroscopy technique. It is shown, that to get useful information out of the device, 

admittance should be measured below 100 kHz. Above this cut-off frequency the device will 

not respond and the obtained signals are meaningless. The analysis of measured capacitancevoltage 

characteristics allowed us to determine the doping concentration in ZnO at the level of 

ND = 7.3×10 17 cm -3 , via the corresponding Mott-Schottky plot. 

Using capacitance transient measurements working at 10 kHz (performed with an HP 

4275A LCR bridge), four majority-carrier deep levels were identified, the most important one 

at approximately 0.5 eV below the conduction band edge with a density about two orders of 

magnitude below the doping level (NT = 4×10 15 cm -3 ). The others, located at 0.2 eV, 0.66 eV 

and 0.75 eV, are about three orders of magnitude below the doping level (NT = 4–9×10 14 cm -3 ). 

[1] F. D. Auret, S. A. Goodman, M. Hayes, M. J. Legodi, H. A. van Laarhoven, D. C. Look, 

Appl. Phys. Lett. 79, 3074 (2001). 

[2] Y.-P. Wang, W.-I. Lee, T.-Y. Tseng, Appl. Phys. Lett. 69, 1807 (1996). 

Acknowledgements 


Development Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08) and by 

grant of the National Science Center of Poland (1669/B/H03/2011/40). 

206

40th _______________________________________________________________ 


Electrical characterization of the ZnO-based Schottky diodes for possible 

sensor applications 

Tomasz A. Krajewski 1 , Adam J. Zakrzewski 1 , Grzegorz Łuka 1 , Łukasz Wachnicki 1 , 

Sylwia Gierałtowska 1 , Bartłomiej S. Witkowski 1 , Piotr Kruszewski 1 , 

El bieta Łusakowska 1 , Rafał Jakieła 1 , El bieta Guziewicz 1 1, 2 

, Marek Godlewski 



Cardinal S. Wyszy ski University, ul. Dewajtis 5, 01-815 Warsaw, Poland 

Zinc oxide is currently widely investigated as a very promising II-VI semiconducting 

material for various electronic and optoelectronic purposes. The ZnO applications include 

mainly solar cells, where it acts as a transparent electrode as well as the new generation of 3D 

memories built in the so-called cross-bar architecture, in which the ZnO-based Schottky diode 

plays a role of a selecting element. The ZnO-based junction can also be used as a gas or 

organic compounds’ sensor. 

In this work we report on fabrication and characterization of the ZnO-based Schottky 

diodes dedicated for the latter application. The junctions were fabricated using the low 

temperature Atomic Layer Deposition (ALD) process, in which the Si, ITO-covered glass and 

glass substrates were uniformly covered with the ZnO film in a double exchange reaction 

between diethylzinc and deionized water. Finally, on the obtained ZnO layer the Ag Schottky 

contact was evaporated. 

Interestingly, the examined diodes exhibit the reversible effect on their current-voltage 

characteristics under treatment with different organic liquids (acetone, isopropanol). As this 

behavior is not observed e.g. under their exposure to water, we deduce that the structures can 

be effectively used for sensing of the organic molecules. 

The obtained current-voltage characteristics were analyzed within the thermionicemission 

theory. In this way the values of some relevant diodes’ parameters were determined, 

including the ideality factor and Schottky barrier height. We found a satisfactory agreement of 

experimental and theoretical results what will be demonstrated during the conference. 

Acknowledgements 


Development Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08) and by 

grant of the National Science Center of Poland (1669/B/H03/2011/40). 

207

WeP32 _______________________________________________________________ 


Ab initio calculations of transition metal impurity levels in III-V 


T. Zakrzewski and P. Bogusławski 

Institute of Physics, Polish Academy of Sciences, Al. Lotników32/46, 02-668 Warsaw, Poland 

Properties of transition metal impurities in semiconductors attract a considerable 

attention both from the fundamental point of view, and in the context of possible applications 

in fabrication of devices. In particular, from the theoretical point of view an important 

problem is the role and the correct description of the electron-electron interactions of delectrons. 

We have analyzed the electronic structure of Mn and Fe impurities in GaP and GaN. 

The calculations were performed within the density functional theory, using both the 

generalized gradient approximation and the Hubbard "+U "corrections, as implemented in the 

Quantum Espresso code. We have also employed the supercell approach, with supercells 

containing 128-atoms including the impurity. The obtained results are compared with the 

available experimental data, and a good agreement is obtained even without inclusion of the 

+U corrections. Moreover, we theoretically investigate the fulfillment of the Langer-Heinrich 

rule. 

208

40th _______________________________________________________________ 


Anisotropy of GaMnAs thin film. Planar and Anomalous Hall measurements. 

P. Juszyński 1 , D. Wasik 1 , M. Baj 1 , J. Przybytek 1 , M. Gryglas-Borysiewicz 1 , J. Sadowski 2,3 

1 Faculty of Physics, University of Warsaw, Hoża 69, 00-681 Warsaw, Poland 


3 Max-Lab, Lund University, Lund, SE-221 00, Sweden 

The search for appropriate semiconductor base materials for spintronic applications is 

a challenge of a last few years. Ga1-xMnxAs which reveals ferromagnetic behaviour at low 

temperatures is a natural candidate for such material. Its magnetic anisotropy is one of the 

most important features for possible applications of this material. It is well known that 

temperature [1] and strain [2] has influence on anisotropy. The aim of this paper was to study 

temperature dependence of the magnetic anisotropy of 50 nm thin film of Ga1-xMnxAs with 

epitaxial nearly critical strain by means of magnetotransport experimants. The Ga1-xMnxAs 

samples were grown by MBE method on GaAs substrate with InGaAs buffer. 

Standard and planar Hall measurements were 

performed as a function of magnetic field at various 

temperatures. Planar Hall hysteresis loops (Fig 1 up) 

and Anomalous Hall signal (Fig 1 down) were observed. 

We analyzed experimental data using single 

domain model [3], which appeared to be sufficient to 

understand magnetic and transport properties of the 

samples. Uniaxial and cubic anisotropy constants (Ku 

and Kc respectively) were treated as fitting parameters. 

We found that the shape of hysteresis loops strongly 

depends on the Ku , Kc parameters as well as on the 

hallbar alignment with respect to magnetic field. 

Our analysis allowed us to obtain anisotropy 

constants in the temperature range 14K – 60K and to 

find Tc ≈ 70K. 

[1] D. Y. Shin et al, Physical Review B 76, 035327 (2007) 

[2] H. Lee et al, Solid State Communication 149 (2009) 1300-1303 

[3] K. Pappert et al, New Journal of Physics 9 (2007) 354 

209 

RH [ ] 

RH [ 

720 

710 

700 

690 

680 

670 

measurement 

fit 

660 

-0.2 -0.1 0.0 0.1 0.2 

150 

100 

50 

0 

-50 

-100 

-150 

Applied field [T] 

-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 

Applied field [T] 

figure 1 

Planar Hall hysteresis loop (upper panel) 

in temperature 14 K and Anomalous Hall 

Signal (lower panel).

WeP34 _______________________________________________________________ 


Interplay between internal and external electric field studied by 

photoluminescence in InGaN/GaN light emitting diodes. 

G. Staszczak 1 , A. Khachapuridze 1 , S. Grzanka 1,2 , R. Piotrzkowski 1 , R. Czernecki 1,2 , 

P. Perlin 1,2 and T. Suski 1 

1 Institute of High Pressure Physics PAS, Sokołowska 29/37, 01-142 Warszawa, Poland 

2 TopGaN, Sokołowska 29/37, 01-142 Warszawa, Poland 

Efficient light emitting diodes (LEDs) and laser diodes (LDs) consist usually of multi 

quantum wells (MQWs)in their active region. In case of InxGa1-xN/GaN emitters, MQWs with 

identical or different content of In are employed. Due to the presence of internal electric field 

in polar structures and devices with InGaN/GaN QWs reduction in the overlap between 

electron and hole wave functions occur leading to a decrease of the emitted light intensity. In 

nitride LEDs and LDs an additional electric field originating from p-n junction contributes to 

the band edges profiles of the device structure and an involvement of individual QWs to the 

light emission can be tuned by externally applied voltage. This large number of factors 

influencing energy and light emission efficiency makes full understanding of the InGaN/GaN 

LEDs and LDs behavior very difficult. Capability of computer simulations is very limited 

also. 

To improve this unsatisfactory understanding of LEDS and LDs behavior we have 

studied series of polar InGaN/GaN LEDs consisting either blue or combination of blue and 

violet QWs (i.e., with intentionally introduced various content of Indium during metalorganic 

vapor deposition, MOVPE). Moreover, each type of the QW was placed closer or more 

distant from the p-type region of the particular LED. We found that in agreement with 

expectations electroluminescence induced by low currents characterizes light emission from 

QW more distant with respect to Mg-doped part of the structure. Micro photoluminescence 

was used in our studies as a probe supplying an information about the behavior of particular 

QWs subject to external polarization and excited by variable light intensity of He-Ne laser. 

We found that depending on external voltage applied to our LEDs as well as applied laser 

power we could modify drastically intensity of light emitted by our structures. In particular, 

we demonstrated: i) switching-on the observed light emission from one or two QWs, ii) 

evolution of the dominant PL signal intensity between violet and blue QWs. Screening of 

electric field due to different laser intensity supplied an additional parameter capable to tune 

significantly properties of studied structures. Simulations performed by us are in qualitative 

agreement with our experiments and they give an inside into the dependence between 

modification of the bands profile during applying external electric field and density of 

optically injected carriers. 

210

40th _______________________________________________________________ 


Influence of antimony on the optical quality of GaInN:Sb multi quantum 

wells 

M. Baranowski 1 , M. Latkowska 1 , R. Kudrawiec 1 , M. Syperek 1 , J. Misiewicz 1 

G.S Karthikeyan 2 , S. Jong-In 3 , and K.L June 2 

1 Institute of Physics, Wrocław University of Technology, Wyspia skiego 27, 50-370 Wroclaw 

2 Interdisciplinary Program of Photonics Engineering, Chonnam National University, 

Gwangju 500-757, Republic of Korea 

3 Department of Electrical and Computer Engineering, Hanyang University, Ansan 426-971, 

Republic of Korea 

InGaN based semiconductors have attracted recently much attention, especially for 

their application in light emitting devices such as blue and green laser diodes and light 

emitting diodes. InGaN alloy with different In content is able to cover almost whole visible 

spectral range what is very important for the full color media applications. Concentration of In 

in InGaN alloy affects optical quality of this material, for low In content (few percentage) 

enhancement of radiative recombination is observed what is connected with carrier 

localization effects caused by small potential fluctuations. However further increase of 

incorporated In strongly deteriorate optical quality of InGaN layers and QWs. It was shown 

that one of the reason of luminescence degradation is strong increase of QWs and layers 

inhomogeneity and formation of In-reach clusters. Because of that one of the main challenge 

for technologist is to improve growth method of InGaN alloy to increase homogeneity of this 

material. 

In the past few years it has been found that introduction of antimony, during growth of 

GaInNAs and GaN alloy, improves optical quality of this materials. This is because of 

reactive surfactant properties of antimony which reduces the group-III surface diffusion 

length thereby suppress phase segregation and roughening, improving homogeneity. The aim 

of this work is investigation if the presence of antimony in growth process of InGaN alloy 

improve its optical quality, similar as in case of GaInNAs alloy. 

Five InGaN multi-quantum wells (MQW) samples used in this study were grown on 

c-plane sapphire substrate by MOCVD method. QWs was grown on a n-doped GaN buffer 

layer. Structure consist of 5 InGaN/GaN QWs with ~25% of indium content. During the 

growth process of InGaN QW Sb flow with various (Sb)/((In)+(Ga)) ratios was introduced. 

The amount of incorporated antimony vary from 0-0.12%. More detail about samples can be 

found in ref. [1]. To investigate optical properties of samples we have measured 

photoluminescence and time-resolved photoluminescence at different temperatures. We have 

found that antimony has influence on the optical quality of samples. With initial increase of 

antimony content the intensity of photoluminescence and the decay time of 

photoluminescence increases and achieve maxim at about 0.05% of antimony content. Further 

increase of antimony content deteriorates optical quality of samples. Additionally we found 

that antimony does not affects the transition energy, all investigated samples emit on a 500nm 

wavelength. Obtained results suggest that properly used antimony can work as a surfactant for 

InGaN alloy and improve its optical quality. 

[1] Karthikeyan Giri Sadasivam, Jong-In Shim, and June Key Lee, Journal of Nanoscience 

and Nanotechnology Vol. 11, 1787–1790, (2011). 

211

WeP36 _______________________________________________________________ 


Properties of Mn-doped GaAs Nanowires and GaAs/(Ga,Mn)As Core-Shell 

Nanowire Structures Grown by MBE on GaAs(111)B Substrates 

J. Sadowski 1,2 , A. Siusys 2 , P. Dziawa 2 , A. Reszka 2 , B. J. Kowalski 2 

1 MAX-Lab, Lund University, P.O. Box 118, 221 00 Lund, Sweden 

2 Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warszawa, 

Poland 

During the last decade a huge research activity has been devoted to the bottom-up approach of 

formation of nanostructures, in which the nanoscale structures are fabricated by self 

assembled growth. This is due to the remarkable progress in the growth methods of quasi-1dimensional 

structures - nanowires (NWs), which can now be grown from many different 

semiconducting materials. Usually the growth of NWs is initiated by nanodroplets of a 

catalyst (usually gold) deposited at the planar substrate used for the NWs deposition, 

however, depending on the material, also autocatalytic or catalyst-free NW growth can be 

achieved. The NWs can be grown with a use of methods applied so far for planar growth such 

as molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD), 

only slight modifications of the growth conditions and the special substrates (prepatterned 

and/or covered with a suitable catalyst) are needed to change the growth mode from 2dimensional 

(formation of layers) to 1-dimensional (formation of nanowires). 

Here we report on use of the NW growth techniques, namely gold catalyzed NW growth to 

formation of 1-D nanostructures implying GaMnAs ferromagnetic semiconductor. The NWs 

were grown by MBE on GaAs(111)B substrates covered with a thin (1 nm) gold layer. The Au 

layer is converted to the ensemble of nanodroplets by initial preheating of the substrate to 

about 600 o C in the MBE growth chamber, and then the NWs are grown at the substrate 

temperature of about 550 o C. Two types of NW structures were investigated: (i) GaAs NWs 

doped with Mn at high temperature (550 o C) MBE growth, (ii) core shell structures with high 

temperature grown GaAs core NWs and low temperature (250 o C) grown GaMnAs shell. The 

scanning electron microscopy images of the latter type of structure are shown in Fig.1. 

Figure 1. Scanning electron microscopy pictures of Au-catalysed GaAs-GaMnAs core-shell nanowires 

grown on GaAs(111)B substrate. The NWs grow along [111] direction perpendicular to the substrate. 

The Mn doping of GaAs NWs during high temperature MBE growth usually results in 

disordered NWs with branches and different orientations, caused by MnAs segregation and 

catalyzing properties of MnAs nanoislands. Structural and magnetic properties of both types 

of samples will be compared, in search of NWs with appropriate magnetic properties. 

This work has been partially supported by the EC Network SemiSpinNet (PITN-GA-2008-215368) 

212

40th _______________________________________________________________ 


Room temperature nano-magnetism of (Ga,Fe)N films: 

element specific spectroscopy and microscopy 

I.A. Kowalik 1 , M.A. Niño 2 , A. Locatelli 3 , T. Onur Menteş 3 , A. Navarro-Quezada 4 , 

Mauro Rovezzi 4 , A. Bonanni 4 , T. Dietl 1,5 and D. Arvanitis 6 


2 IMDEA, Facultad de Ciencias Módulo C-IX, Madrid, Spain 

3 Sincrotrone Trieste, Basovizza, Trieste, Italy 

4 Institut für Halbleiter-und-Festkörperphysik, J. Kepler University, Linz, Austria 

5 Institute of Theoretical Physics, University of Warsaw, Warsaw, Poland 

6 Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden 

We present results of magnetic investigations at room temperature on (Ga,Fe)N films 

by means of soft x-ray based element specific and spin sensitive spectroscopy [1]. The studied 

samples were grown by MOVPE and studied previously by SQUID magnetometry, 

transmission electron microscopy, synchrotron radiation based x-ray diffraction techniques, 

[2,3] as well as by EXAFS and XANES [4]. In order to establish a relationship between the 

nanocrystal structure and their magnetic properties we carried out laterally averaged 

measurements of XMCD and XLMD, and further spatially resolved by means of 

photoemission microscopy (PEEM) with magnetic resolution (XMCD-PEEM) at the Fe Ledges 

and XMCD at the N-K edge. 

We complement these results by means of more systematic element specific and 

dichroic spectro-miscroscopy measurements, using synchrotron radiation soft x-rays as the 

excitation source. The laterally resolved chemical characterization with X-PEEM at the Fe Ledges 

indicate that Fe is incorporated both in Ga substitutional sites in the GaN lattice, as well 

as in self-assembled FeNx nanocrystals. We can identify typical nanocrystal sizes from about 

30 nm to 150 nm, depending on the growth conditions. In samples grown under specific 

conditions, we observe also FeGa and GaFeN nanocrystals. This chemical imaging confirms 

that the Fe atoms are embedded in different local environments. By means of XMCD-PEEM 

we identify magnetic Fe-rich nanocrystals and can visualize the magnetic domain state of 

each nanocrystal. A first analysis indicates that often the nanocrystal magnetic moments can 

order following a curling magnetic structure (vortex). Comparing chemical and magnetic 

micrographs within the same field of view, allows identifying the existence of both 

ferromagnetic and non-ferromagnetic nanocrystals. An XLMD signal is found for these 

samples, indicating that the existence of anti-ferromagnetic nanocrystals contributes to the 

absence of ferromagnetism in XMCD-PEEM. The present set of data illustrates the 

complementarity of X-PEEM and XMCD-PEEM, with angle dependent, XAS, XMCD and 

XLMD measurements without spatial resolution, on the same samples. 

Acknowledgments 

We acknowledge the EC support through the FunDMS Advanced Grant of the ERC within the 

"Ideas" 7th Framework Programme, the Austrian Fonds zur Förderung der wissenschaftlichen 

Forschung-FWF (P18942, P20065 and N107-NAN), the Swedish Research Council, the EC 

Seventh Framework Programme (FP7/2007-2013) under grant agreement Nr 226716 (ELISA) 

for access to MAX-lab and Elettra. 

[1] I.A. Kowalik et al., Phys. Rev. B, in press [arXiv: 1011.0847]. 

[2] A. Bonanni et al., Phys. Rev. B 75, 125210 (2007); Phys. Rev. Lett. 101, 135502 (2008). 

[3] A. Navarro-Quezada et al., Phys. Rev. B 81, 205206 (2010). 

[4] M. Rovezzi et al., Phys. Rev. B 79, 195209 (2009). 

213

WeP38 _______________________________________________________________ 


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WeP40 _______________________________________________________________ 


Spin-Polarized STM with Fe-Coated W Tips and Bulk Cr Tips 

E.P. Smakman, R. van Voornveld, J.G. Keizer, J.K. Garleff, P.M. Koenraad 

Our goal in this project is to use spin-polarized scanning tunneling microscopy (SP-STM) to study 

magnetic nano-structures in metals and semiconductors. As a proof of concept, I present measurements 

on a metal surface which has been studied previously [1]: a W(110) crystal covered with 1.5 ML Fe. The 

crystal has step edges and plateaus of roughly 7 nm wide. A plateau is divided in a single layer wire (1 

ML) and a double layer wire of Fe (2 ML), because of the step flow growth method. By also coating the 

W tip in situ with several ML Fe, the tip is made spin sensitive. By means of a lock-in amplifier, 

differential conductivity data is obtained from the surface, which contains both electronic and magnetic 

information. The single and double layer wires of Fe on the surface show a different contrast in the data. 

Additionally, nearby single layer wires are shown to be antiferromagnetically ordered, which is a sign 

that our tip is sensitive for in-plane magnetization of the surface. With bulk Cr tips also spin-sensitive 

contrast is observed, showing double layers with an alternating magnetization. These spin-sensitive tips 

open up the possibility to study magnetic semiconductors on the atomic scale. 

216 

[1] O. Pietzsch, Phys. Rev. Lett. 84, 5212 (2000).

40th _______________________________________________________________ 


Cathodoluminescence measurements at liquid helium temperature 

of monocrystalline ZnO layers 

B.S. Witkowski 1 , Ł. Wachnicki 1 , E. Guziewicz 1 , M. Godlewski 1,2 



Cardinal S. Wyszy ski University, Dewajtis 5, 01-815 Warsaw, Poland 

ZnO is a II-VI semiconductor which has a direct energy gap of 3,37eV at room temperature 

[1,2] and a high exciton binding energy (60meV). High transparency allows application of 

ZnO as an electrode in solar cells [3], but also as an active part of transparent transistor, crossbar 

memories, etc. Due to these properties ZnO is an attractive material for photovoltaic, 

electronic and optoelectronic devices. 

In recent works we showed, that high quality ZnO layers can be obtained by the Atomic Layer 

Deposition at fairly low temperature of 300°C [4]. In the present work we discuss results of a 

Cathodoluminescence (CL) measurements of these films which were performed at 

temperature of 5K. CL is synchronized with Scanning Electron Microscopy (SEM), so we can 

image luminescence of the same area as in the SEM images. These measurements give 

information about uniformity of films and local potential fluctuations resulting in exciton 

localization. We searched for an inter-link between microstructure of the films and their 

optical properties. Role of localization effects will be demonstrated. 



References: 

[1] C. Klingshirn, Phys. Status Solidi, B 244 (9) (2007) 3027. 

[2] S.J. Pearton, D.P. Norton, K. Ip, Y.W. Heo, T. Steiner, Superlattices Microstruct. 34 (2003). 

[3] M. Godlewski, E. Guziewicz, G. Łuka, T. Krajewski, M. Łukasiewicz, Ł. Wachnicki,, A. 

Wachnicka, K. Kopalko, A. Sarem, B. Dalami, Thin Solid Films 518 (2009) 1145. 

[4] Ł. Wachnicki, T. Krajewski, G. Łuka, B. Witkowski, B. Kowalski, K. Kopalko, J.Z. Domagala, M. 

Guziewicz, M. Godlewski, E. Guziewicz, Thin Solid Films 518, 16, 4556-4559 (2010) 

217

WeP42 _______________________________________________________________ 


Towards electrically controllable read-write devices based on 

ferromagnetic semiconductors 

T. Andrearczyk 1 , I. Krogulec 1,2 , T. Wosi ski 1 , T. Figielski 1 , A. M kosa 1 , Z. Tkaczyk 1 , 

J. Wróbel 1 and J. Sadowski 1,3 


2 College of Science, Cardinal S. Wyszynski University, 01-815 Warsaw, Poland 

3 MAX-Lab, Lund University, 22100 Lund, Sweden 

The idea of writing and reading digital information in a single compact device, using 

electric current, is extremely attractive. A class of such devices can be based on the effect of 

displacement of magnetic domain walls (DWs) caused by electric current in ferromagnetic 

semiconductors. The (Ga,Mn)As epitaxial layers, becoming ferromagnetic at low 

temperature, offer a good model material for such devices. This is due to several merits, 

among which a relatively low critical current density for DW motion is one of the major 

importance. An essential ingredient of such devices is the magnetic anisotropy caused by 

patterning-induced strain relaxation, which introduces an additional degree of freedom that 

can be used in device operation. In our preliminary investigations we examined two types of 

nanostructures fabricated from (Ga,Mn) As ferromagnetic layers. One of them has been the 

three-arm nanostructure [1], and the other – the cross-like nanostructure composed of two 

perpendicular nanostripes crossing in the middle of their lengths [2,3]. The latter structure is 

especially interesting as it allows, in principle, for full electrical control of the device. The 

underlying idea is that the magnetization in a nanostripe is forced to be directed along its long 

axis, while in the area of stripes intersection it is determined rather by the crystalline 

anisotropy of parent layer. Domain walls separating regions of different magnetization 

directions contribute an extra resistance to the total electrical resistance of a nanostripe in a 

rate depending on the spin misalignment. Manipulating the magnetization directions in the 

stripes by means of an external magnetic field, or electric current passing through the stripes, 

allows reaching either of two electrical states of each stripe that distinguish themselves by 

different resistances. In the present work we have studied those effects in more details using 

cross-like naostructures fabricated from Ga0.94Mn0.06As layers, grown by the low-temperature 

molecular-beam epitaxy method, and next patterned by the electron-beam lithography and 

chemical etching. We interpret the obtained results in terms of DWs rearrangement and also 

discuss the contribution of anisotropic magneto-resistance to the observed effects. 

This work has been partially supported by the Polish Ministry of Science and Higher 

Education under Grant No. N N202 129339. 

[1] T. Figielski, T. Wosi ski, A. Morawski, A. M kosa, J. Wróbel, and J. Sadowski, Appl. 

Phys. Lett. 90, 052108 (2007). 

[2] T. Andrearczyk, T. Wosi ski, T. Figielski, A. M kosa, J. Sadowski, Z. Tkaczyk, E. 

Łusakowska and J. Wróbel, Acta Phys. Pol. A 114, 1049 (2008). 

[3] T. Andrearczyk, T. Wosi ski, A. M kosa, T. Figielski, J. Wróbel, and J. Sadowski, Acta 

Phys. Pol. A 116, 901 (2009). 

218

40th _______________________________________________________________ 


Magnetic properties of Mn-ion implanted and plasma pulse treated Si 

J. B. Gosk 1, 2 , Z. Werner 3 , C. Pochrybniak 3 , M. Barlak 3 , J. Szczytko 1 and A. 

Twardowski 1 

1 Institute of Experimental Physics, Warsaw University, Ho a 69, 00-681 

Warsaw, Poland 

2 Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 


3 The Andrzej Soltan Institute for Nuclear Studies (IPJ) 

05-400 Swierk/Otwock, Poland 

The race for a room temperature ferromagnetic semiconductors for spintronic 

applications continues for about a decade. Although many different materials have been 

synthesized and studied so far, the highest Curie temperatures (TC) are is still below room 

temperature demanded for commercial applications. There is a hope that ion implantation 

methods, routinely used in manufacturing of integrated circuits, could overcame a problem of 

low solubility limits of magnetic ions in magnetic semiconductors. In this context very 

promising seems to be the technique using plasma pulses allowing simultaneously both 

magnetic ion implantation and melting/regrowth of crystals. 

Here, we report on silicon implanted with Mn ions. Three types of samples were 

prepared basing on p-type Si(100) single-crystal wafers. The first type (denoted as Asamples) 

were implanted at room temperature with 2·10 +16 cm -2 of 190 keV Mn + ions. They 

were next treated with 4J/cm 2 of hydrogen plasma pulses of duration of about 1 s. The Mnion 

implanted Si but not treated by hydrogen plasma (denoted as B- samples) were used as 

reference samples. The third type of samples (denoted as C-type samples) were pulse Mn 

implanted in the Rod Plasma Injector (RPI) in the Deposition by Pulse Erosion (DPE) mode. 

The samples were RBSc analysed using 1.7 MeV He + beam at Rossendorf Van de 

Graaff accelerator. It appears that Mn implanted region recrystallizes as an epitaxial layer and 

that Mn atoms occupy interstitial positions, both after ion implantation and after pulse plasma 

treatment. 

Magnetic measurements of all the samples were performed using a SQUID 

magnetometer in the temperature range 2-300 K and magnetic fields (B) up to 7 T. In general 

magnetization (M) of all the samples consists of two components: a paramagnetic (PM) one 

and a ferromagnetic (FM) contribution. Similarly as in [1] FM contribution shows TC higher 

than room temperature. The relative abundance of FM contribution is the largest for Asamples 

(about one third of total magnetization at B=7 T), smaller for B-samples (about a 

quarter of total M at B=7 T) and the smallest for C-samples (about 4% of total M at B=7 T). 

PM contribution reveals typical Brillouin-type behavior: strong temperature dependence, 

pronounced tendency to saturation with magnetic field at low temperatures, and linear field 

dependence at high temperatures. For both A- and B-samples magnetization nearly saturates 

at B=7 T and T=2K, while for C-sample apparently 7 T is not enough to saturate M. All the 

samples show history dependence: there is a pronounced difference between Field Cooling 

and Zero Field Cooling protocols, different for A-, B- and C-samples. Such behavior suggests 

anisotropy effects present for manganese magnetic centers. These effects will be related to 

samples’ preparation procedures. 

[1] M. Bulduc at. all., Phys. Rev. B 71, 033302 (2005) 

219

WeP44 _______________________________________________________________ 


Simulations of optical modes in InGaN based laser diodes operating at 

455 nm 

G. Muzioł 1,2 , M. Siekacz 2 , H. Turski 2 , C. Skierbiszewski 2 

1 Faculty of Applied Physics and Mathematics, Gdansk University of Technology, 

Gabriela Narutowicza 11/12, 80-233 Gdansk, Poland 

2 Institute of High Pressure Physics, Unipress, Sokolowska 29/37, 01-142 Warsaw, 

Poland 

Nitride based laser diodes (LDs) which cover the emission wavelengths from ultraviolet 

to the green region recently become a subject of intensive studies. The emission wavelength 

can be engineered by changing the indium composition in the quantum wells - one can shift 

the emission wavelength from ultra-violet up to green [1]. For a successful operation of LDs 

not only perfect structural quality of grown layers is crucial but also the reduction of the 

optical losses in the laser structure is of the great importance. 

In this work we study a new design for waveguide (WG) and cladding layers (CL) for 

nitride based true-blue LDs operating at 455 nm to reduce optical losses. We calculate the 

influence of composition and thickness of WG and CL on the confinement factor and internal 

losses of a LDs. A one-dimensional method developed by M. J. Bergmann and H. C. Casey Jr. 

[2] is used for numerical determination of the transverse electric field distribution. Parameters 

for calculations were taken from Ref [3]. We demonstrate how the thickness of upper cladding 

layer affects the internal losses. For too thin claddings the mode reaches the highly absorptive 

upper gold contact which causes unnecessary losses. 

By changing the composition of waveguide we can significantly modify the operating 

parameters of a LD. We show a comparison between two waveguide designs: a) 180 nm GaN 

waveguide, b) 180 nm GaN with internal 90 nm InGaN high refractive index waveguide. The 

second design not only gives a higher confinement factor but also lowers the internal losses 

caused by magnesium doped cladding and gold contact. In case of the waveguide without 

indium the mode leaks to the substrate which negatively affects the far-field pattern [4]. The 

design with an internal InGaN waveguide eliminates this phenomenon. In conclusion, we 

demonstrated that proper design of the waveguides and claddings reduces the optical losses in 

the contact layer and the substrate. We will compare the one dimensional model prediction 

with more general two-dimensional method developed by U. Schwarz et al. [5]. 

Acknowledgements: This work was supported partially by the Polish Ministry of 

Science and Higher Education Grant No IT 13426 and the European Union within European 

Regional Development Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08). 

[1] J. Wu, W. Walukiewicz, K. M. Yu, J. W. Ager III, E. E. Haller, Hai Lu and William J. 

Schaff, Appl. Phys. Lett. 80, 4741 (2002). 

[2] M. J. Bergmann and H. C. Casey Jr., Journal of Applied Physics, 84(3):1196–1203, 

1998. 

[3] G. M. Laws, E. C. Larkins, I. Harrison, C. Molloy, and D. Somerford, J. Appl. Phys., 

89(2):1108–1115, 2001. 

[4] L. A. Coldren and S. W. Corzine. Diode Lasers and Photonic Integrated Circuits. 

Willey Interscience, 1995. 

[5] U. T. Schwarz and B. Witzigmann, “Optical properties of edge-emitting lasers: 

measurement and simulation”, Nitride Semiconductor Devices, edited by J. Piprek, Wiley- 

VCH 2007. 

220

40th _______________________________________________________________ 


Monte-Carlo simulations and magnetic studies of ferromagnetic 

nanocomposites. 

Magdalena Woińska 1,2 , Karolina Madrak 2 , Jacek Szczytko 1 , Jacek Gosk 1,3 , Andrzej 

Majhofer 1 , Damian Pociecha 2 , Ewa Górecka 2 , Andrzej Twardowski 1 



2 Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland 

3 Faculty of Physics, Warsaw University of Technology, 

Koszykowa 75, 00-662 Warsaw, Poland 

It has been reported that thermal annealing of Ga1-xMnxAs layers leads to formation of 

MnAs dots [1] and that in MOVPE-grown (Ga,Fe)N ferromagnetic FeNx nanocrystals aggregate 

by precipitations like GaxMny, MnxNy or FexNy [2]. Usually these precipitations form 

(nano)crystals of different size and orientation embedded in semiconductor matrix. Such 

nanocomposites are promising candidates for information storage and spin electronics 

applications [3]. The analysis of magnetic properties of such semiconductor-based 

nanocomposites is a complex task because of difficulties in the control over the size of 

ferromagnetic nanoclusters and the distance between them. Usually these nanoprecipitations have 

a broad distribution of theirs diameters and one cannot change and control independently size and 

concentration of them. They consist of small and usually single domain (superparamagnetc) and 

large multiple domain (ferromagnetic) nanocrystals. Thus, in order to test theoretical models and 

numerical approaches, one may look for systems where at least crystals’ size distribution is 

narrow. Having a theoretical approach which describes well such model magnetism one can adapt 

it to the more complex semiconductor-based materials 

Ferromagnetic cobalt nanoparticles immersed in a solid organic medium can be a model 

system for such investigations. In this work we present a Monte-Carlo study of such structures. 

The zero field cooling – field cooling (ZFC/FC) sequences were measured as a function of the 

size (6 nm and 11 nm) and concentration of nanoparticles. The experimental results are compared 

with Monte-Carlo simulations of magnetism of such nanocomposites. The comparison between 

the magnetism of: isolated, interacting and aggregated nanoparticles will be discussed. 

[1] J. Sadowski, et al., Appl. Phys. Lett. 87, 263114 (2005) 

[2] A. Bonanni, et al,. Phys. Rev. B 75, 125210 (2007), Phys. Rev. Lett. 101, 135502 (2008). 

[3] T. Dietl et al., Phys. Rev B 63, 195205 (2001) 

221

WeP46 _______________________________________________________________ 


Di-TEMPO amine for molecular spintronics – model of p-shell magnetism. 

Jacek Szczytko 1 , Jadwiga Szydlowska 2 , Nevill Gonzalez Szwacki 3 , Konrad 

Dziatkowski 1 , Paweł Giziński 1 , Andrzej Kaim 2 , Andrzej Twardowski 1 



2 Department of Chemistry, University of Warsaw, 

Al. Żwirki i Wigury 101, 02-089 Warsaw, Poland 

3 Institute of Theroretical Physics, Faculty of Physics, University of Warsaw, 


Growing interest in spintronics and spin control on the atomic level arises from predicted 

superiority of the spin of the electron over the electron charge in terms of energy and speed 

efficiency. Advances in this field require a new approach to the concept of spin manipulation 

and new magnetic materials. Most of the solution are based on magnetic metals and 

semiconductors with localized magnetic moments on the d-shell. However one can induce 

magnetic properties also on the p-shell which is occupied by single electron forming a free 

radical or two p-shell electrons in triplet state. It is probable that p-shell magnetism is 

responsible for a high magnetic moment in Gd-focused ion-beam-implanted GaN [1]. 

The bottom-up strategy for spintronics can only be realized by extensive studies of spin 

interactions in well defined clusters of atoms or molecules. In this communication we present 

the study of antiferromagnetic coupling between two free radicals localized in di-TEMPO 

amine structure. 

We present the results of electronic spin resonance (EPR), SQUID magnetometry, X-ray 

diffraction and theoretical investigations carried out using the NWChem code suite [2]. Our 

model compound – di-TEMPO possess the property of adjustable lattice structure, depending 

on the type of solvent in which molecular crystal was precipitated. Still, within the accuracy 

of measurements, modifications of the external structure of the compounds don’t seem to 

affect in a significant manner the magnetic properties of the di-TEMPO complex, which seem 

to depend solely on the internal structure the compounds. For the other hand theoretical 

prediction of exchange interaction gives two order of magnitude greater value of this 

interaction than observed by SQUID magnetometry, which suggest that p-p interaction is 

diminished by the interactions with neighboring atoms in a crystallized sample. The 

interaction between magnetic single occupied electronics orbitals (SOMO) in the crystal 

lattice will be discussed and compared with experimental results of spin resonance and spinspin 

interaction. 

[1] S. Dhar, T. Kammermeier, A. Ney, L. Pérez, K. H. Ploog, A. Melnikov, and A. D. Wieck, Ferromagnetism 

and colossal magnetic moment in Gd-focused ion-beam-implanted GaN Appl. Phys. Lett. 89, 062503 (2006); 

[2] E. J. Bylaska et al., NWChem, A Computational Chemistry Package for Parallel Computers, Version 5.1.1 

2008). 

222

40th _______________________________________________________________ 


Hopping excitons in GaInNAs alloys: Radiative versus non-radiative 

recombination at various temperatures 

M. Baranowski, M. Latkowska, R. Kudrawiec, and J. Misiewicz 

Institute of Physics, Wrocław University of Technology, Wybrze e Wyspia skiego 27, 


Incorporation of a few percents of nitrogen atoms into Ga(In)As host (i.e., forming dilute 

nitrides) strongly affects its band structure and optical properties, i.e., the energy gap is 

strongly reduced and the electron effective mass is increased. In addition, nitrogen atoms 

deteriorate optical properties of Ga(In)As host and some characteristic features appear for this 

material in photoluminescence (PL) spectra at low temperatures. Usually the spectra are very 

broad and asymmetric. The temperature dependence of PL peak energy exhibits a deviation 

from Varshni’s formula, i.e., so called S-shape behavior. These features are usually explained 

by the recombination of excitons localized on some potential fluctuations. In 1998 

Baranovskii at al. have proposed a model of hopping excitons in semiconductors [1] and 

recently this model has been applied to dilute nitrides [2]. However the main spectral motive 

observed in near-field PL and micro-PL spectra (i.e., the sharp PL lines) was not simulated so 

far by this model. Recently we have introduced some changes to this model and applied such 

a modified model to explain the origin of sharp lines observed in micro-PL spectra of 

GaInNAs layers and their changes with the excitation power and temperature [3]. Instead of 

two types of recombination centres (radiative and non-radiative centres) introduced by 

Baranovskii we have proposed one kind of localization centres with the radiative and nonradiative 

rates. Such a modification is justifiable due to our recent experimental observations 

for GaInNAs alloys [4] and allows us to explain the fast thermal quenching of localized 

emission from this alloy. Our simulations clearly show that the individual sharp PL lines 

observed at low temperatures appear for this material due to exciton hopping between 

localization centres. Taking into account saturation effects and exciton dissociation 

phenomenon it has been shown that the observed changes in power- and temperaturedependent 

-PL spectra can be excellently reproduced by the modified model. In this work we 

will focus on simulations of PL spectra obtained at various temperatures for different 

excitation powers for GaInNAs alloys with a different concentration of localizing centers 

which are related to deep donor(acceptor)-like states. These simulations clearly show that 

these states are responsible for weak PL intensity from GaInNAs alloys at room temperatures. 

The authors acknowledge support from the MNiSW (grant no. N202 258339). 

[1] S. D. Baranovskii, et al., Phys. Rev. B 58, 13081 (1998). 

[2] O. Rubel, et al., Phys. Rev. B 73, 233201 (2006). 

[3] M. Baranowski, et al., J. Physics: Cond. Matter, in press (2011). 

[4] M. Latkowska, et al., Appl. Phys. Lett. 98, 131903 (2011). 

223

WeP48 _______________________________________________________________ 


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Admittance spectroscopy in GaNp-n junction 

P. Kamyczek 1 , E. Popko 1 , Z. Gumienny 1 , E. Zielony 1 , S.Grzanka 2,3 , R. Czernecki 2,3 , 

T. Suski 3 

1 Institute of Physics, Wroclaw University of Technology, WybrzezeWyspianskiego 27, 


2 TopGaN Ltd., Sokolowska 29/37, 01-142 Warszawa, Poland 

3 Institute of High Pressure Physics ‘UNIPRESS’, Polish Academy of Sciences, Sokolowska 

29/37, 01-142 Warszawa, Poland 

P-n GaN junctions grown by metal-organic vapor-phase epitaxy technique (MOVPE) 

on Ga-polarity (0001) surface of GaN substrates were investigated using frequency-dependent 

capacitance–voltage measurements and admittance spectroscopy. Admittance spectroscopy 

(AS) is frequently used to characterize deep impurities in semiconductors. It indeed gives 

direct access to the emission–capture processes occurring between an impurity level and the 

conduction or the valence band. A defect state in the band gap leads to a decrease of 

capacitance and an appearance of the peak in the curves of conductance/frequency versus 

frequency. Through the temperature dependence of the position of this peak, the energy 

activation level can in principle be deduced from corresponding Arrhenius plot. This 

technique is an alternative method to the deep level transient spectroscopy (DLTS) 

extensively exploited in characterization of defects in semiconductors. However if a deep 

level cannot follow the high frequency voltage modulation (DLTS is usually based on a 1 

MHz capacitance bridge meter) this technique fails. 

For the samples under study the capacitance versus bias (C-V) and AS measurements 

were performed at temperatures ranging from 300K down to 20K and for frequencies between 

10 2 and 3x10 6 Hz. The room-temperature C-V measurements yield apparent free carrier 

concentration NC-V in the order of 2.6 x10 18 cm -3 irrespective to the applied frequency. On the 

other hand, the capacitance vs frequency (C-f) curve exhibits strong frequency dependence, 

implying the presence of traps of concentration . Within the temperatures 

ranging from 300K down to 140K, a single relaxation maximum is visible on the 

conductance/frequency versus frequency plot. At lower temperatures another peak emerges. 

Additionally it was found that the external bias does not affect the plots. Thus it may be 

assumed that the peaks are related to point defects. Activation energies for the peaks obtained 

from corresponding Arrhenius plot are equal to 86±5 meV and 5±0.5meV respectively for the 

high and low temperature peak. The high temperature peak is presumably related to Mg deep 

acceptor state whereas the low-temperature peak to carrier freeze-out. The energy of Mg 

related state is lower than found elsewhere [1,2] however this discrepancy may be linked with 

the Poole-Frenkel effect [3]. Presence of internal field related to p-n junction significantly 

lowers trap energy obtained from AS in the case of high doping level, like in the case of the 

studied samples. Obtained results are complementary to the DLTS measurements run by us on 

the same sample [4] yielding additional source of information on defects in the studied p-n 

GaN junctions. 

[1] E. Monroy et al., Appl. Phys. Lett.74, 1171 (1999). 

[2] J. W. Huang et al., Appl. Phys. Lett.68, 2392 (1996). 

[3] D. J. Kim, J. Appl.Phys. 88, 1929 (2000). 

[4] E. Płaczek-Popko et al., Physica B: Physics of Condensed Matter, 404, 4889 (2009). 

226

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Role of hydrogen in the ammonia based growth of GaN and 

InGaN - ab initio study 

Pawel Kempisty 1 , Pawel Strak 1 , and Stanislaw Krukowski 1,2 

1 Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 


2 Interdisciplinary Centre for Materials Modeling, Warsaw University, Pawinskiego 5a, 


Growth of GaN and GaInN nitrides by ammonia based method, such as hydride vapor 

phase epitaxy (HVPE) and metal organic vapor phase epitaxy (MOVPE) relies on 

the ammonia decomposition providing active nitrogen and also hydrogen at the crystal 

surface. Using ab intio density functional theory simulations, a basic scenario of molecular 

processes was derived. It is shown that adsorption of molecular hydrogen on bare 

GaN(0001) surface leads to its dissociation and location of H atoms in the sites, above 

the Ga surface atoms. The process strongly depends on the coverage, being strongly 

exothermic for coverage lower and endothermic for higher than 0.75 ML. It is shown that 

adsorption of ammonia on bare or hydrogen covered surface, is barrierless and occurs 

in the molecular form leading to mixed NH2 and NH3 coverage, as some of the excess 

hydrogen is desorbed in the form of H2 molecules. This coverage can be shifted towards 

ammonia by additional flux of molecular hydrogen. It is calculated that molecular hydrogen 

overcomes adsorption barrier of about 1 eV, dissociating at the surface and converting 

NH2 radicals into NH3 admolecules. Thus the ammonia coverage may be dominant in the 

hydrogen rich ambient. The adsorption of metal adatoms, Ga and In, strongly depends 

on the surface coverage type, being stable for the coverage dominated by NH2 radicals 

and unstable for coverage dominated by NH3 admolecules. 

The research was supported by the European Union within European Regional Development 

Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08). 

227

WeP52 _______________________________________________________________ 


Effect of the built-in strain on the in-plane optical anisotropy of 

m-plane GaN/AlGaN quantum wells 

S.P. ̷Lepkowski 1 , W. Bardyszewski 2 , and H. Teisseyre 3 

1 Institute of High Pressure Physics, “Unipress”, Polish Academy of Sciences, 

ul. Soko̷lowska 29/37, 01-142 Warszawa, Poland 

2 Institute of Theoretical Physics, University of Warsaw, ul. Hoza 69, 00-681 Warszawa, 

Poland 

3 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 

02-668 Warszawa, Poland 

Group III-nitrides heterostructures grown along nonpolar directions of the wurtzite 

structure (corresponding to a-plane or m-plane) are attractive for applications and basic 

research due to the lack of built-in electric fields and the presence of large in-plane optical 

anisotropy [1]. The built-in strain caused by the lattice mismatch between the quantum 

well and the substrate may further enhance the anisotropy of the emitted light polarization. 

This effect may be exploited as a tool for studying the light - matter coupling in 

semiconductor lasers and microcavities. 

In the present study we investigate theoretically the influence of the built-in strain 

on the electronic structure and optical transition oscillator strengths for the m-plane 

GaN/AlGaN quantum wells grown on AlGaN substrates with different aluminum contents. 

The anisotropic built-in strain is calculated by applying the linear theory of elasticity 

and assuming that the structure is pseudomorphic. Energy levels and electronic 

wave functions are obtained by using the finite element method to diagonalize the k · p 

Rashba - Sheka - Pikus Hamiltonian for the valence band. The conduction band levels 

were obtained in the parabolic approximation. The parameters for AlxGa1−xN are estimated 

using the linear interpolation between binaries except for the energy gap and 

the spontaneous polarization for which bowing is taken into account as in Ref. 2. The 

calculations were performed for a 5 nm GaN/Al0.2Ga0.8N quantum well grown on the 

AlxGa1−xN substrate with x less than 0.5. 

Inthecaseofunstrainedquantumwells, i.e. forx = 0, thelowestenergytransition(c1v1) 

corresponds to the valence band level with the Γ9 symmetry and the next transition 

(c1-v2) is associated with Γ7 symmetry. Therefore, the oscillator strength of the c1-v1 

transition is large for the in-plane polarization perpendicular to the c axis and much 

smaller for the polarization parallel to the c-axis. On the other hand, the next transition 

c1-v2 is dominant for the polarization parallel to the c axis and almost negligible for the 

polarization perpendicular to the c axis. 

With increasing Al content x in the substrate all transition energies increase and so 

does the energy separation between the c1-v1 and the c1-v2 transitions. At the same 

time the oscillator strength for the c1-v1 transition decreases for the in-plane polarization 

perpendicular to the c axis and increases for the polarization parallel to the c-axis. The 

opposite occurs for the c1-v2 transition. As the result, by increasing the concentration of 

Al in the substrate from x = 0 to x = 0.5 one can change the polarization of the emitted 

light with respect to the c-axis by 90 degrees. 

[1] P. Misra, O. Brandt, H. T. Grahn, H. Teisseyre, M. Siekacz, C. Skierbiszewski, and 

B. ̷Lucznik, Appl. Phys. Lett. 91, 141903 (2007). 

[2] S. P. ̷Lepkowski, J. A. Majewski, and G. Jurczak, Phys. Rev. B 72, 245201 (2005). 

228

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Magnetooptical properties of (Ga,Fe)N layers 

J. Papierska 1 , J.-G. Rousset 1 , A. Golnik 1 , W. Pacuski 1 , M. Nawrocki 1 , J. A. Gaj 1 , 

J. Suffczy ski 1 , I. Kowalik 2 , W. Stefanowicz 2 , M. Sawicki 2 , T. Dietl 1,2 , A. Navarro-Quezada 3 , 

B. Faina 3 , Tian Li 3 , A. Bonanni 3 

1 Faculty of Physics, University of Warsaw, Warsaw, Poland 

2 Institute of Physics Polish Academy of Sciences, Warsaw, Poland 

3 J. Kepler University of Linz, Austria 

Numerous works on diluted magnetic semiconductors carried out over the last decade 

have aimed in examining intricate interplay of ferromagnetic and semiconducting properties 

[1]. Wide band gap semiconductors such as GaN and ZnO doped with magnetic ions are 

particularly interesting in view of their wide ranging applications. Here we present results of 

magnetic circular dichroism (MCD) and Magneto-optical Kerr effect (MOKE) measurements 

in the excitonic spectral region performed on (Ga,Fe)N layers. In contrast to previous 

magnetooptical studies [2], we focus here on possible magnetoptical signatures of Fe-rich 

nanocrystals that appear in (Ga,Fe)N films obtained under suitable growth conditions [3]. 

We compare magnetoptical properties of two layers with similar concentrations of 

paramagnetic Fe ions (3×10 19 cm -3 and 2×10 19 cm -3 , respectively), one containing Fe-rich 

nanocrystals, the other not, according to extensive SQUID, XRD, and HRTEM 

characterization. As found in SQUID measurements, the sample with Fe-rich nanocrystals 

reveals a ferromagnetic response persisting up to above room temperature for two orientations 

of the magnetic field in respect to the c-axis. Reflectivity and MOKE measurements are 

performed in the Faraday configuration with the c-axis parallel to the incident beam in the 

magnetic field up to 7 T at 2 K. The sample is illuminated by a Xe lamp. 

We find that the field dependent magnitudes of MCD and Kerr rotation angle in the 

excitonic region are well descried by the paramagnetic Brillouin function in both samples. 

This means that ferromagnetic features, clearly seen in SQUID magnetometry, are not 

contributing to the magnetooptical response. We conclude that either character of nanocrystal 

magnetoptical properties or the nanocrystal distribution and density are not optimized to result 

in sizable magnetoptical phenomena. Instead, the presence on Fe-rich nanocrystals reduces 

the magnitude of the paramagnetic-like magnetooptical signals. In line with this observation, 

we find that a large magnetooptical response can be recovered by Ar sputtering of the sample 

surface, the finding consistent with the location of nanocrystals near the film surface [3]. 

[1] T. Dietl et al., Science 287, 1019 (2000); Nature Mater. 9, 965 (2010). 

[2] W. Pacuski et al., Phys. Rev. Lett. 100 (2008) 037204 

[3] A. Bonanni et al., Phys. Rev. Lett. 101, 135502 (2008); A. Navarro-Quezada et al., Phys. 

Rev. B 81, 205206 (2010). 

The work was supported by FunDMS Advanced Grant of ERC within the Ideas 7th FP of EC, 

NCBiR project LIDER, and InTechFun (Grant No. POIG.01.03.01-00-159/08). 

229

WeP54 _______________________________________________________________ 


Gas Phase Reactions during GaN Growth by MOVPE Method – Ab initio 

Study 

Maria Ptasinska 1 , Jacek Piechota 1 , Jakub Sołtys 1 , and Stanisław Krukowski 1,2 

1 Interdisciplinary Centre for Materials Modeling, University of Warsaw, Pawi skiego 5a, 02- 

106 Warsaw, Poland 

2 Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 


Ab initio density functional theory (DFT) simulations were used to determine basic reaction 

during growth of gallium nitride by Metal Organic Vapor Phase Epitaxy (MOVPE) method, 

using trimethylgallium (TMG - Ga(CH3)3) and ammonia (NH3) as active sources of gallium 

and nitrogen, respectively. DFT based commercial codes were used: for the simulations of 

molecular reaction in the vapor – Dmol3 [1,2] and for reactions at the solid surfaces -VASP 

[3,4]. The decomposition of the TMG and the liberation of methyl groups are necessary steps 

for incorporation of gallium into GaN. The two possible scenarios of these processes were 

taken into consideration, either assuming reaction with ammonia in the vapor, or TMG 

adsorption and consecutive reaction. Calculations showed that the creation of GaN:NH3 

compound is energetically possible in the gas phase and energy needed to create that 

compound was calculated. Also the behavior of the TMG in hydrogen environment as well as 

energy needed for direct release the CH3 radials from TMG molecule was obtained. 

Simulation of the GaN surface, either covered by hydrogen or by ammonia admolecules or by 

NH2 radicals, indicate that TMG shows remarkable durability at GaN(0001) surface, which is 

enhanced by the change of electrostatic charge at the surface. Therefore, the decomposition of 

TMG at the surface is difficult, which suggest that dominant role is played by the vapor phase 

reactions, either by thermal decomposition of TMG or by reaction with ammonia leading to 

creation of the complex molecules which could enhance liberation of methyl groups and 

incorporation of gallim into GaN crystal. 


Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08 and POIG.01.03.01-14- 

155/09). 

[1] B. Delley, J. Chem. Phys. 92, 508 (1990). 

[2] B. Delley, . J. Chem. Phys. 113, 7756 (2000). 

[3] G. Kresse, and J. Hafner, Phys. Rev. B 47, 558 (1993); ibid. 49, 14 251 (1994). 

[4] G. Kresse, and J. Furthmüller, Comput. Mat. Sci. 6, 15(1996). 

[5] G. Kresse, and J. Furthmüller, Phys. Rev. B 54, 11169 (1996). 

230

40th _______________________________________________________________ 


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231

WeP56 _______________________________________________________________ 


Density Functional Theory (DFT) simulations of the physical properties of 

AlN/GaN multiple quantum wells (MQWs) 

Pawel Strak 1 , Pawel Kempisty 1 , Konrad Sakowski 1 , and Stanislaw Krukowski 1,2 * 

1 Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 


2 Interdisciplinary Centre for Materials Modeling, Warsaw University, Pawi skiego 5a, 02- 

106 Warsaw, Poland 

Ab initio DFT simulations of AlN/GaN multiquantum wells (MQW) were used to obtain 

physical properties of the system. By appropriate averaging procedure an electric potential 

profile was obtained showing the existence of strong electric field in the wells and barriers 

and additionally revealing a new phenomenon of electric potential jumps at the interfaces. 

The fields and the potential jumps were used to obtain density of the polarization charges and 

the magnitude of the dipole layer at AlN/GaN heterointerfaces, respectively. It was shown 

that polarization dipoles are confined within single double atomic layers, proving that they are 

of different nature from the dipole layers emerging at the semiconductor surfaces or within pn 

junctions. Band structure analysis is used to obtain the change of the quantum states energy 

in electric field confirming existence of Quantum Confined Stark Effect (QCSE). The 

mechanical stress influence was accounted for by systematic changes of the lattice constant 

from AlN to GaN, assuming that the system is conformal with the substrate. It is shown that 

the stress affects strongly not only polarization fields but also the magnitude of dipole layers 

at AlN/GaN heterointerfaces. 


Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08 and POIG.01.03.01-14- 

155/09). 

232

40th _______________________________________________________________ 


Plasma-assisted MBE growth and characterization of GaN nanocolumns on 

Si (111) Substrates 

Z.R. Zytkiewicz, P. Dluzewski, J. Borysiuk, M. Sobanska, K. Klosek, 

B. Witkowski, P. Nowakowski, and J. Dabrowski 

Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02 668 Warsaw, Poland 

There is current interest in the development of electronic devices based on nanowires or 

nanocolumns made of wide bandgap semiconductors. Due to possibility of charge localization 

by quantum confinement and low density of structural defects use of nanocolumns is 

promising for optoelectronic applications. Moreover, a high surface to volume ratio makes 

crystalline nanostructures a topic of intense research in sensor applications. 

In this work we report on growth of GaN nanocolumns (NCs) on (111) silicon substrates 

by plasma assisted MBE (PAMBE). Riber Compact 21 system equipped with elemental 

source of Ga and an Addon RF plasma source of active nitrogen was used for the growth. The 

growth started by deoxidation of Si (111) substrate followed by its exposure to a nitrogen flux 

at temperature of 790 o C. Then, self-organized growth of nanocolumns started at ~750 o C 

under highly nitrogen-rich conditions. No catalyst was used to induce nucleation of NCs. 

Fig. 1 shows SEM birds-view image of the sample grown for 90 minutes. An ensemble 

of GaN NCs is clearly visible. Typically, they are ~350 nm long with diameter of 20 – 30 nm. 

It is noteworthy that the nanocolumns are homogenously distributed and well oriented with 

the c-axis being perpendicular to the substrate. Fig. 2 shows cross-sectional TEM image of the 

sample while Fig. 3 presents high-resolution TEM image of the interface between Si(111) and 

the GaN nanocolumn (magnification of the rectangular area in Fig. 2). Presence of ~2 nm 

thick film of amorphous SixNy between GaN and the substrate is clearly visible. Despite that 

GaN is perfectly epitaxially aligned to the Si(111) substrate. Moreover, no wetting layer is 

seen that indicates that NCs are grown spontaneously by Volmer-Weber mechanism [1]. Low 

temperature photoluminescence and cathodoluminescence were used to study optical 

properties of GaN NCs. 

GaN NCs 

Si (111) 

Fig.1: SEM image of GaN NCs sample 

taken under a declination angle of 20 o . 

[1] J. Ristic et al. J. Crystal Growth 310 (2008) 4035. 

Si 

GaN 

20 nm 

This work was partly supported by the European Union within European Regional 

Development Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08 

NanoBiom). 

GaN 

Fig. 2: TEM image of GaN 

nanocolumns. 

233 

Fig. 3: TEM image of the interface 

between Si(111) and GaN nanocolumn.

WeP58 _______________________________________________________________ 


Crossing Size Limits of Bulk III-V Crystals Feasible by Liquid Phase 

Electroepitaxy 

Zbigniew R. Zytkiewicz 1 , Pawel Strak 2 , and Stanislaw Krukowski 2 

1 Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02 668 Warsaw, Poland 

2 Institute of High Pressure Physics, Polish Academy of Sciences, ul. Sokolowska 29/37, 

01 142 Warsaw, Poland 

Liquid phase electroepitaxy (LPEE) is a crystal growth method in which the DC electric 

current passing through the solution-substrate interface is the driving force for crystallization 

while temperature of the system is kept constant. LPEE has been found to be very effective 

for the growth of bulk crystals of multicomponent semiconductors. In particular, the LPEE 

grown crystals show compositional uniformity that is not attainable by other solution or melt 

growth methods (see [1] for a review). Unfortunately, as shown experimentally [2] and 

theoretically [3, 4] thickness of crystals feasible by LPEE is limited to ~3-4 mm. This is due 

to Joule heating in the body of growing crystal, which finally leads to complete termination of 

the growth. In this work we present a new design for the growth of bulk III-V crystals by 

electroepitaxy which avoids severe drawbacks of standard LPEE. In the technique, that we 

name contactless LPEE (CLPEE), the electric current still being the main mechanism of 

solute transport, does not flow through the solution/seed interface. By proper arrangement of 

the current flow, the Joule heating of the growing crystal is eliminated. Thus the main obstacle 

on the road to long duration processes necessary to obtain bulk multicomponent substrate 

crystals, paving the route to new method of the growth of crystals from solution is proposed. 

CLPEE method of growth from the liquid solution is modeled using finite volume (FV) 

commercial Fluent code. This allowed us to study how distributions of temperature, electric 

potential, solute concentration and growth rate depend on geometry of the growth cell, time 

and electric current density. We consider the case of CLPEE of GaAs as an example of the 

growth of III-V semiconductors. This is because for the Ga-As/GaAs system values of many 

material parameters required by the model are easily available. It should be noted, however, 

that the growth technique proposed can be used for other crystals too and extension of the 

model for other materials is straightforward if values of these parameters are determined. 

[1] T. Bryskiewicz, Prog. Crystal Growth and Characterization 12 (1986) 29. 

[2] Z.R. Zytkiewicz, J. Crystal Growth 146 (1995) 283. 

[3] Z. R. Zytkiewicz, J. Cryst. Growth 172 (1997) 259. 

[4] P. Strak, Z.R. Zytkiewicz, K. Sakowski, and S. Krukowski, Cryst. Res. Technol. 45 (2010) 

1290. 

This work was partially supported by the Polish Ministry of Science and Higher Education 

(grant N N507 280636) and by the European Union within European Regional Development 

Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08 NanoBiom). 

234

40th _______________________________________________________________ 

"Jaszowiec" 2011 International School and Conference on the Physics of Semiconductors ThI1 

Quantum Cascade Lasers 

Maciej Bugajski 1,2 , Kamil Kosiel 1 , Anna Szerling 1 , Piotr Borowik 2 , 

Leszek Adamowicz 2 , Grzegorz Hałda 3 , Andrzej Kolek 3 

1 Institute of Electron Technology, Al. Lotników32/4, 02 668 Warsaw, Poland 

2 Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 

00 662 Warsaw, Poland 

3 Department of Electronics, Rzeszów University of Technology, W. Pola 2, 

35 959 Rzeszów, Poland 

The quantum cascade lasers (QCLs) are unipolar devices based on tunneling and 

intersubband transitions, in which the electronic states, wavefunctions and lifetimes of 

relevant states are engineered through the quantum mechanical confinement imposed by a 

complex multilayer structure. The second main feature of this type of lasers is the cascading 

scheme of carriers route through the laser active region. For QCLs to work, the extremely 

precise tailoring of energy levels of quantum states, optical dipole matrix elements, tunneling 

times and scattering rates of carriers is required. 

Thus the principle of operation of QCL structures places stringent requirements on the 

individual layer thickness and composition as well as the overall periodicity of the whole 

structure. The laser operation is possible only when the designed structure is strictly realized, 

with the extreme technological precision concerning geometrical and doping features. 

Another crucial problem of QCLs’ operation are the heating effects, which are distinctly 

larger than in the state-of-the-art bipolar lasers. This is connected with the processes of 

depopulation of the lower laser level and carrier thermalization in the injector, by scattering 

with the optical or acoustic phonons. The heating results in the higher threshold and operation 

currents of the lasers, and all this in turn results in the necessity of the effective heat 

extraction. The heat dissipation in QCLs is strongly hampered because of the nature of their 

active regions containing many interfaces, and layers with thickness similar to the mean free 

path of phonons. 

In this lecture we will present the development of mid-infrared GaAs/AlGaAs QCLs 

technology and discuss basic characteristics of lasers fabricated at the Department of 

Photonics at the Institute of Electron Technology [1-4]. We will also show that reliable 

simulation methods which can deal with the complicated physical phenomena involved in the 

quantum cascade lasers operation are necessary tools to predict the behavior of new structures 

and optimize their performance. We will briefly discuss Monte Carlo approach to modelling 

electron transport in QCLs [5,6] and nonequlibrium Green’s function formalism [7]. 

[1] K. Kosiel, M. Bugajski, A. Szerling, Photonics Letters of Poland, 1, 16 (2009) 

[2] M. Bugajski, K. Kosiel, A. Szerling, Bulletin of the Polish Academy of Sciences; 

Technical Sciences 58, 471 (2010) 

[3] K. Pier ci ski, D. Pier ci ska, K. Kosiel, A. Szerling, M. Bugajski, Journal of Electronic 

Materials, 39, 630 (2010) 

[4] K. Kosiel, M. Bugajski, A. Szerling, Terahertz and Mid Infrared Radiation, NATO Science 

for Peace and Security Series B: Physics and Biophysics, Chapter 13, Springer (2011) 

[5] P. Borowik, J.L. Thobel, M. Bugajski, L. Adamowicz, Acta Physica Polonica, 116, 49 

(2009) 

[6] P. Borowik, J.L. Thobel, Leszek Adamowicz, Journal of Applied Physics, 108, 073106 

(2010) 

[7] G.Hałda , A. Kolek, M. Bugajski, Optoelectronics Review, in print (2011) 

235

ThI2 _______________________________________________________________ 


New Concepts and Materials for Solar power Conversion Devices 

Wladek Walukiewicz* 

1 Materials Sciences Division Lawrence Berkeley National Laboratory**, 1 Cyclotron Road, 

Berkeley, CA 94720, USA 

In the presentation I will introduce various new concepts for high efficiency conversion of 

solar energy. The core presentation will focus on two research areas: group III-nitrides for 

high efficiency multijunction solar cells and highly mismatched alloys for multiband solar and 

photoelectrochemical cells. 

The discovery of the low band gap of InN greatly expanded the range of the direct gaps of 

group III-nitride alloys from 0.64 in InN to 6.1 eV in AlN. Therefore In1-xGaxN and In1-yAlyN 

alloys are promising materials for high efficiency solar cells, as their band gaps are 

continuously tunable across the solar spectrum. The potential of In1-xGaxN as a solar cell 

material has been well established and there has been a significant worldwide effort aimed at 

practical application of this material system for photovoltaic devices. The large electron 

affinity (5.8 eV) of InN offers a unique opportunity of matching the conduction band edge of 

group III-In-nitride alloys to the valence band of standard semiconductors such as Si and Ge. 

Thus n-type In1-xGaxN with x=0.55 or In1-yAlyN with y=0.3 form “ideal” low resistance 

junctions with p-type Si. Calculations show that two junction InGaN/Si or AlInN/Si tandem 

cells could have practical power conversion efficiencies exceeding 35%. The low resistance 

contact between n-InGaN and p-Si has been demonstrated for InGaN films grown on Si with 

GaN as well as Al thin buffer layers. Latest results on practical realization of InGaN/Si 

tandem cells will be presented and remaining challenges will be discussed. 

The second part of the presentation will be devoted to recent progress in synthesis of 

highly mismatched alloys (HMAs). Such alloys exhibit unusual optical and electrical 

properties and with a proper choice of component materials allow for an independent 

engineering of band gaps and band offsets. We have synthesized group II-VI dilute oxides 

and group III-V dilute nitride HMAs. The alloys have a unique band structure with a narrow 

intermediate band in the band gap of the host material. The band serves as a “stepping stone” 

allowing pairs of sub-bandgap photons to contribute to the solar light induced photo-current, 

leading to better utilization of the full solar spectrum. Ongoing efforts to produce simple, 

single junction high efficiency cells based on these alloys will be presented. I will also 

present most recent results on successful synthesis of GaNAs alloys in the whole composition 

range and discuss potential use of these materials in photoelectrochemical cells for solar water 

dissociation. 

*In collaboration with Solar Energy Materials Research Group (http://emat-solar.lbl.gov/) 

**Supported by the Division of Materials Science and Engineering, US DOE 

236

40th _______________________________________________________________ 


ZnO biosensing 

Danek Elbaum 

Institute of Physics, Polish Academy of Science, Warsaw, Poland 

ZnO nanocrystals have recently attracted a lot of attention as promising candidates for 

novel devices, due to a possibility of continuous tuning of optical and electronic properties by 

varying the particle sizes. They are also of interest for pharmaceutical industry, medicine 

and/or biology. 

ZnO nanostructures were obtained using two diverse methods: sol-gel and 

electrospinning. We have explored nanocrystals of ZnO/MgO as potential intracellular 

sensors. Synthesized nanocrystals were characterized structurally by AFM, TEM, X-ray 

diffraction and optically by absorption and emission. Addition of MgO shell resulting in a 

more intense and stable visible emission that is characteristic of nanocrystalline ZnO. XRD 

patterns of powdered ZnO/MgO nanocrystals and TEM data proved wurtzite crystalline 

structure. A temperature sensitive Fluorescence Resonance Transfer (FRET) was observed 

between ZnO/MgO (donors) and Nile Red (acceptor) when linked by beta-carboxymethyl 

cyclodextrin molecules. 

Electrospinning is a method capable to produce fibers with diameters ranging from 

tens of nanometer to microns, possessing interesting photoelectrical properties.. Electrospun 

nanofibrous scaffolds have great potential in several biomedical applications, such as wound 

dressing, enzyme immobilization, drug delivery, tissue engineering, and they can serve as 

materials for extracellular biosensors. We constructed a FET detector taking advantage of 

the electric conduction properties of ZnO nanofibers. 

237

ThI4 _______________________________________________________________ 


Nitride laser diodes 

Piotr Perlin, Katarzyna Holc 

Institute of High Presure Physics PAS 

TopGaN, Ltd. 

InGaAlN laser diodes have been first realized more than 15 years ago and their 

technology acquired enough maturity to make possible the development of new, advanced 

applications. I would like to mention here full color display technologies, including laser TV 

and movie theater projectors, printing, medical and biosensing applications. The process of 

matching nitride laser diodes parameters to these expected by the new application produces a 

strong bias for even stronger effort to understand the basic limitation and advantages of a 

complicated physical systems formed by III-N semiconductors. During this presentation I will 

briefly review the recent advancement in the field focusing specially on couple of specific 

problems like: 

Substrates for laser diodes epitaxy 

Design and fabrication of laser diode waveguide 

InGaN quantum wells from UV to green 

Novel devices, new concepts 

238

40th _______________________________________________________________ 


Application of CdSe quantum dots for single photon emitters 

at room temperature 

D. Hommel 1 , C. Kruse 1 , T. Kümmell 2 , O. Fedorych 2 , G. Bacher 2 

1 Institute of Solid State Physics, University of Bremen, Germany 

2 CeNIDE, University Duisburg-Essen, Germany 

Solid state single photon sources are central devices for quantum information 

technology. A variety of concepts has come up during the last years, mostly based on colloidal 

quantum dots, color centers and on self organized semiconductor quantum dots (QDs). The 

latter are especially attractive, as they can be easily integrated into electrically driven devices. 

But a drawback has to be noted: While electrically driven sources of single and even 

entangled photons have been implemented, these devices are based mainly on the InGaAs or 

the InGaP material system, and therefore the operation temperature is limited to temperatures 

below 100 K. 

In contrast, for operation under ambient conditions wide-bandgap II-VI quantum are 

expected to be ideally suited: They inherently provide a much better carrier confinement and 

higher exciton binding energies compared to Ga(In)As. In addition it could be shown that 

electrically driven CdSe-QD laser diodes under pulsed excitation have a sufficient lifetime 

[1]. Therefore this system should be be a good candidate for single photon emission at room 

temperature (RT). Optimizing the carrier confinement in CdSe QDs by adding thin MgS 

barriers and ZnSSe of high sulfur concentration highly efficient RT emission from single 

quantum dots has been reported by us both under optical [2] and electrical operation [3]. 

We now report for the first time on single photon emission from a single, epitaxially 

grown quantum dot up to room temperature. For the devices, self organized CdSe quantum 

dots grown by molecular beam epitaxy are formed in a similar structure within ZnSSe and 

2nm MgS barriers to provide high quantum efficiency at elevated temperatures. Nanoapertures 

down to 150 nm allow for addressing single quantum dots. 

In photoluminescence, we can track the single quantum dot emission up to room 

temperature, with the intensity of the emission decreasing by a factor of only 3 between 4 K 

and 300 K. In accordance with earlier findings [2], we detect a significant broadening of the 

emission lines up to nearly 28 meV due to exciton-phonon interaction. Fine structure effects 

have been studied as well [4]. 

Photon correlation measurements were performed using a Hanbury-Brown-Twiss- 

Setup. Even under continuous wave excitation, a striking antibunching behavior is found up to 

T = 300 K. Second-order correlation measurements reveal a surprisingly low value of g (2) ( ) = 

0.15 for zero time delay even at room temperature, confirming the high potential of these 

quantum dots for future single photon emitting devices operating under ambient conditions. 

[1] A. Gust et al., phys. stat. sol (c) 2, 1098 (2005) 

[2] R. Arians el al., Appl. Phys. Lett. 90, 101114 (2007) 

[3] R. Arians el al., Appl. Phys. Lett. 93, 173506 (2008) 

[4] T. Kümmell et al., Phys. Rev. B 81, 241306 (2010) 

239

ThI6 _______________________________________________________________ 


Terahertz Emitters Based on GaN/AlGaN HEMTs 

W. Knap, N.Dyakonova, D. Coquillat, F. Teppe 

TERALAB - Université Montpellier 2 and CNRS,Montpellier, 34090, FRANCE 

The channel of High Electron Mobility Transistor can act as a resonator for the 

plasma waves propagating in 2D electron gas. The plasma frequency increases with reduction 

of the channel length and can reach the Terahertz range for nanometre size transistors. As it 

was predicted by Dyakonov and Shur 1 , when a current flows through a field effect transistor, 

the steady state can become unstable against generation of plasma waves leading to the 

emission of an electromagnetic radiation at the plasma wave frequencies. It was also 

predicted 2 that nonlinear properties of the 2D plasma in the transistor channel can be used for 

resonant and voltage tuneable detection 2 of THz radiation. In this work we present an 

overview of experimental results on THz detection and emission by GaN/AlGaN 

nanotransistors. An overview of the subject can be found in Ref [3,4] 

We will present recent results on THz emission obtained in different types of 

GaN/AlGaN nanometric high electron mobility transistors [5]. We show that depending on 

the transistor geometry different THz emission mechanism play role. In field plate HEMTs in 

agreement with the theoretical predictions i) the emission frequencies correspond to the 

estimated characteristic plasma wave frequencies and ii) the emission appears once the drain 

current exceeds a certain well defined threshold value. First results have been obtained at 

cryogenic temperatures , however recently it was shown that from nanometer gate length 

GaN/AlGaN transistors one can also obtain an efficient room temperature THz emission [5]. 

Possible aplications of GaN HEMTs as THz sources will be discussed. 

[l] M. I. Dyakonov, M. S. Shur, “Shallow water analogy for a ballistic field effect transistor: 

New mechanism of plasma wave generation by dc current”, Phys. Rev. Lett. 71, 2465 (1993). 

[2] M. I. Dyakonov, M. S. Shur, “ Plasma wave electronics: novel terahertz devices using two 

dimensional electron fluid,” IEEE Trans. Electron Devices 43, 380 (1996). 

[3] W. Knap, F. Teppe, N. Dyakonova, D. Coquillat, J Łusakowski, ”Plasma wave 

oscillations in nanometer field effect transistors for terahertz detection and emission”, J. 

Phys.: Condens. Matter 20, 384205 (2008). 

[4] W. Knap, M. Dyakonov, D. Coquillat, F. Teppe, N. Dyakonova, J. Łusakowski, K. 

Karpierz, G. Valusis, D. Seliuta, I. Kasalynas, A. El Fatimy, T. Otsuji, “Field Effect 

Transistors for Terahertz Detection: Physics and First Imaging Applications”, J. Infrared Milli 

Terahz Waves 30, 1319 (2009). 

[5] A. El Fatimy, N. Dyakonova, Y. Meziani, T. Otsuji, W. Knap, S. Vandenbrouk, K. 

Madjour, D.Théron, C. Gaquiere, M. A. Poisson, S. Delage, P. Pristawko, C. Skierbiszewski, 

AlGaN/GaN high electron mobility transistors as a voltage-tunable room temperature terahertz 

sources J. of Appl. Phys. 107, 024504 (2010). 

240

40th _______________________________________________________________ 


Spin transfer torque in TMR and GMR nanostructures for spintronic 

devices 

Tomasz Stobiecki and Witold Skowro ski 

AGH University of Science and Technology, Department of Electronics, al. Mickiewicza 30, 

30-059 Kraków, Poland 

First widely used spintronic device was the Giant Magnetoresistive Spin-Valve (GMR-SV) 

sensor which exhibits large changes in electrical resistance in the presence of the magnetic 

field. The GMR-SV consist of two ferromagnetic layers separated by a thin metallic spacer 

layer. By designing the structure so that even a faint external magnetic field would change the 

relative magnetic orientations of the ferromagnetic layers, the GMR devices became a very 

sensitive magnetic-field sensor used as read-head in a new generation hard disc drives. 

More prospective multilayer system is so called Magnetic Tunnel Junction (MTJ) which 

consists of two metal ferromagnetic electrodes separated by an ultra thin layer of insulator 

(about 1-2 nm typically, amorphous Al-O or crystalline MgO). Many groups have been 

steadily improving the properties of Al-O and MgO barrier MTJs, so that the tunnel 

magnetoresistance (TMR) ratio has been increasing year by year. Recently the TMR ratio 

measured at room temperature has reached 700% in MgO based MTJs. 

By passing high density spin-polarized current through GMR-SV or MTJ nanopillars the Spin 

Transfer Torque (STT) effect is observed. This effect can induced precession of magnetization 

vector or switch the magnetization of the free layer. Spin transfer torque magnetic RAM 

(STT-RAM) has the advantages of lower power consumption and better scalability over 

conventional MRAM. Crucial issues of STT in MTJs are a reduction of the critical current 

density, which is necessary for switching the junction and a reduction of the resistance area 

(RA) product. Making the ultra thin MTJ tunnel barrier, below 1 nm, is one of the approaches. 

In this talk the influence of the MgO barrier thickness on the STT effect in MTJs with a MgO 

wedge barrier will be discussed. The typical multilayer stack of MTJ for STT-RAM 

applications is composed of: Si/Si-ox substrate/ buffer layers/ PtMn(16) antiferromagnet/ 

Co70Fe30(2)/Ru(0.9) synthetic anti-ferrimagnet/ Co40Fe40B20(2.3) bottom electrode (reference 

layer) / MgO(0.6 - 1) tunnel barrier/ Co40Fe40B20(2.3) top electrode (free layer) / protection 

layers (thickness in nm). Elliptical shaped nanopillars with RA product ranging from 2 to 10 

m 2 , sizes of 120 nm × 230 nm and TMR values of up to 160% were prepared by electron 

beam lithography, ion beam milling and lift-off. Current induced magnetization switching of 

the free layer (top electrode) was observed. The critical current density was 10 6 A/cm 2 order 

of magnitude. 

The application of RF current to a nanosized MTJ generate DC voltage across the device, 

when the frequency is in resonance with resistance oscillations, arising from the STT. Such 

spin torque ferromagnetic resonance (ST-FMR) excitation in a MTJ nanopillar, as well as an 

inverse effect, i.e., generation of the RF signal, when MTJ is supplied with DC current, 

provide potential application in the telecommunications technology. 

Project supported by the Foundation for Polish Science MPD Programme, co-financed by the EU European 

Regional Development Fund, SPINSWITCH MRTN-CT-2006-035327 and Ministry of Science and Higher 

Education, grants (NN 515544538 and IP 2010037970). 

241

ThI8 _______________________________________________________________ 


Si-based MEMS devices 

Jan Dziuban 

Wrocław University of Technology, Poland 

242

40th _______________________________________________________________ 


Abstract 

Giant photoconversion on silicon derived materials 

Z.T. Kuznicki 

Photonic Systems Laboratory, Boulevard Sébastien Brant, BP 10413, 67400 Illkirch, France 

tel: +(33) 3 90 24 46 07, fax: +(33) 3 90 24 46 19, email: zbigniew.kuznicki@lsp.u-strasbg.fr 

Invited/oral 

One of the most challenging topics of today’s research and development concerns the efficiency of the light-toelectricity 

conversion, and this obviously on Si-derived devices. The best of the possible/imaginable solutions 

has to allow overcoming the indirect Si bandgap constraints. This aim becomes realizable by transforming the 

hard photon-matter interaction by a soft photon-electron-electron one due to additional new low-energy 

mechanisms allowing a multistage conversion cycle. Such effects have been observed by us within new Si 

derived metamaterials obtained by multiple transformations leading to a nanoscale Si-layered system. In such 

systems, a giant photoconversion could be observed for the first time due to hot electron interactions with active 

interfaces and conditioned crystalline defects representing tectons (unities of the Si metamaterial). Today it 

seems to be the best way to overcome conversion shortages of the bulk, of the thin-film or of any Si based 

converter. We present in this work a background and experimental demonstrations of giant photoconversion. 

Keywords: giant photoconversion, Si derived metamaterial, light-to-electricity conversion cycle, multiinterface 

device, nanoscale Si-layered system, photon-carrier and photon-carrier-carrier interactions, low-energy 

generation and multiplication, multistage conversion, collection efficiency exceeding unity. 

CE (%) 

100 

80 

60 

40 

20 

400 nm 

W00-C10 

W02-C11 

W04-C10 

W14-C10 

W14-C11 i-01 

W14-C12 

LP-06-C2 

LP-07-C6 

LP-08-C4 

W11-C2 

W11-C3 

W11-C5 

W11-C6 

0 

1E+11 1E+12 1E+13 1E+14 1E+15 

TRANSMITED PHOTON NUMBER 

IQE (%) 

160 

100 

135 % 

transmited @ 400 nm 

W09-C10 

40 

1E+12 1E+13 1E+14 1E+15 

AVERAGE TRANSMITED PHOTON NUMBER (cm-2) 

Examples of non-linear CE (IQE) of test devices containing a metamaterial in their superficial nanostratum. The 

curves result from the 400 nm band IQE peak variation versus incident light intensity in different devices (a). 

Saturation appears under the weak photon flux of about 8x10 13 photons/s/cm 2 (b). This is an example of the 

record PV conversion on the Si-based material with 1.35 electrons per incident photon. The average reflection is 

on the order of X%. The whole low energy generation/multiplication effect appears exclusively within the 

superficial stratum. 

243 

Multistage conversion: step-like difference between 

measured and simulated conventional CE (yellow 

diamonds) after optical confinement correction. The 

conventional CE has been simulated using the 

experimental data. The step-like green line results 

from the simulation of carrier multiplication with the 

probability p = 0.8.

____________________ NOTES ____________________ 

244

40th _______________________________________________________________ 


INDEX 

A 

Abdussalam W. TuP14 

Abramof E. MoP24 

Abstreiter G. SaI2 

Adam S. TuI2 

Adamowicz L. ThI1 

Aizpurua J. TuP04 

Albert S. WeO4 

Aleszkiewicz M. MoP01, TuP06 

Alves E. MoP35 

Andrearczyk T. WeP28,WeP42, 

WeP49 

Andrzejewski J. TuP16 

Anisimovas E. MoP05, TuP27 

Antonowicz J. MoP18 

Araki T. WeI4 

Arcade P. TuP50 

Arvanitis D. WeP37 

Aschenbrenner T. TuP34, WeP13 

Atrashchenko A.V. MoP55 

B 

Babi ski A. TuP29,TuP30,TuP32 

Bacewicz R. MoP18 

Bacher G. ThI5 

Baeumler M. WeP20 

Baj M. TuP40, TuP44, 

WeP18, WeP33 

Bajda M. WeP17 

Balakauskas S. MoP53 

Ballester A. TuP33 

Baranowski J.M. TuP03, TuP42, 

TuP44, TuP45 

Baranowski M. WeP22,WeP35, 

WeP47 

Bara ska A. TuP50 

Bara ski J. TuP21 

Barbagini F. WeO4 

Bardyszewski W. WeP08, WeP52 

Barlak M. WeP43 

Bartsch G. TuP36 

Basta M.Ł. MoP49 

Baturin V.A. MoP42, MoP43 

Bauer G. MoP01 

Bayer M. TuP36 

Bednarski H. MoP36, MoP54, 

TuP22 

Bengoechea-Encabo A. WeO4 

Bercha A. WeP17 

245 

Bercha D.M. MoP33 

Bercha S.A. MoP33 

Berthing T. TuP53 

Białek M. TuP39 

Biermann K. TuI4 

Binder J. WeP20 

Birowska M. MoP10, TuO2,WeO3 

Błaszczyk J.A. TuP45 

Bo kowski M. MoP35, WeP07, 

WeP19,WeP38, 

WeP48 

Bogusławski P. WeP04, WeP32 

Bonanni A. WeO2, WeP37, 

WeP53 

Bonde S. TuP53 

Borowik P. ThI1 

Borysiewicz M.A. MoP16 

Borysiuk J. TuP29, TuP44, 

WeP02, WeP20, 

WeP57 

Boukari H. TuP46 

Bracker A.S. TuI1 

Bradley R. TuI4 

Bragar I. TuP26 

Brik M.G. MoP21, MoP35 

Brus V.V. MoP13, MoP26 

Bryant G.W. TuP04 

Bryja L. TuP36, TuP43 

Buczko R. MoO3, MoP02, 

MoP07, TuP10 

Bugaiova M.E. MoP32 

Bugajski M. MoP20, ThI1 

Bujko B. TuP43 

Bukała M. MoP02, MoP07 

Butte R. WeP07 

Buzatu P. TuP38 

Bykov O.I. MoP42, MoP43 

C 

Cabaj A. WeP27 

Calleja E. WeO4 

Cambel V. MoP15 

Campbell P.M. TuP58 

Carter S.G. TuI1 

Cerda-Méndez E. TuI4 

Chegodaev A.D. TuP47 

Chen M.S. MoP48 

Chenaud B. TuP41 

Chèze C. WeP19, WeO6 

Chitta V.A. MoP24 

Chwastek M. MoP36 

Chwastyk M. MoP09 

Consejo C. TuP37, TuP41

_______________________________________________________________ 


Coquillat D. MoO4, ThI6, TuP38, 

TuP41 

Cozan V. MoP54 

Cui K. WeP16 

Cywi ski G. WeO6, WeP19 

Cywi ski Ł. MoP01, TuP01 

Czajkowski G. TuP17 

Czapkiewicz M. TuP06, TuP13, 

TuP39 

Czernecki R. WeP23, WeP34, 

WeP38, WeP50 

D 

Dabrowski J. WeP57 

Dalecki W. MoP08 

DeJaeger B. TuP52 

Devillers T. WeO2 

Di Carlo A. SuI1 

Diduszko R. MoP08 

Dietl T. MoP01, TuO3, WeI2, 

WeO1, WeO2, 

WeO3, WeP01, 

WeP09, WeP15, 

WeP37, WeP53 

Dluzewski P. WeP57 

Dmitriev A.I. MoP34 

Dobkowska S. TuO3, WeP15 

Dobosz D. MoP04, MoP46, 

MoP50 

Domagała J.Z. WeP24, WeP48, 

WeP49 

Doma ski M. MoP36, MoP54 

Doma ski T. MoP58, TuP21 

Dominiak A. TuP45 

Domukhovski V. MoP02 

Doradzi ski R. WeP11, WeP39 

Drabi ska A. MoP03, TuP45 

Droba A. MoP46, MoP50 

Drobiazg T. MoP18 

Drozd V. MoP04 

Drozdziel A. TuP55 

Drube W. MoP47 

Duda H. MoP11, MoP31, 

MoP40, MoP44, 

MoP45, MoP56 

Durygin A. MoP04 

Dusheyko M.G. MoP41 

Dussaigne A. WeP07 

Duzynska A. MoP04 

Dwili ski R. WeP11, WeP39 

Dyakonova N. ThI6, TuP37, TuP38, 

TuP41 

Dybała F. WeP17 

246 

Dybko K. MoP57 

Dyczewski J. MoP16, MoP19 

Dynowska E. MoP16, MoP19, 

MoP51, WeP24 

Dziatkowski K. TuP12, WeP46 

Dziawa P. MoP02, WeP18, 

WeP36 

Dziawa S.P. MoP47 

Dziecielewski I. WeP19 

Dziuban J. ThI8 

E 

Ebeling J. TuP34 

Eddy Jr. C.R. TuP58 

El Fatimy A. TuP38, TuP41 

Elbaum D. ThI3 

Litwin-Staszewska E. WeP55 

Escartín J.M. TuP33 

Evtikhiev V.P. MoP55 

Faina B. WeO2, WeP53 

Fandrich M. WeP13 

Fedorych O. ThI5 

Feduniewicz-Zmuda A. WeP19 

Ferone R. MoO1 

Fidelus J.D. MoP04 

Figge S. TuP34, WeP13, 

WeP30 

Figielski T. WeP42 

Fobelets K. TuP52 

Forchel A. TuP16 

Fronc K. TuP08, TuP13, 

TuP39 

Furman M. WeP06 

F 

G 

Gaj J.A. TuO6, TuP02, 

TuP09, WeP06, 

WeP53 

Galazka R.R. WeP14 

GalickaM. MoO3 

GałkowskiK. WeP06 

Gammon D. TuI1 

Gao Y. TuP12 

Garleff J.K. WeP40 

GasK. MoP47, MoP51 

Gaska R. TuO1

40th _______________________________________________________________ 


Gaskill D.K. TuP58 

Gauthier N. WeP16 

Gawarecki K. TuP25, tuP26 

Gaži S. MoP15 

G gor A. MoP44, MoP45 

Gelczuk Ł. TuP56 

Gierałtowska S. MoP12, MoP19, 

MoP27, WeP31 

Giffard B. MoO4 

Gizi ski P. WeP46 

Gladysiewicz M. WeP39 

Gluba Ł. WeP49 

Glukhov K.E. MoP33 

Godlewski M. MoP12, MoP14, 

MoP27, MoP49, 

WeP06, WeP27, 

WeP30, WeP31, 

WeP41 

Golnik A. TuO5, TuO6, TuP02, 

TuP09, TuP54, 

WeP06, WeP53 

Golub L.E. TuP24 

Gołasa K. TuP29, TuP30, 

TuP32 

Goncharuk G.A. MoO6 

Gonzalez-Szwacki N. WeO1, WeP46, 

MoP59 

Gorczyca I. WeO5 

Goryca M. MoO5, TuO4, TuO5, 

TuP01, TuP09 

Gosk J.B. WeP43, WeP45 

Goss K. WeP23, WeP26 

Go ci ski K. WeP30 

Górecka E. WeP45 

Grabecki G. MoP01 

Grabiec P. TuP37 

Grandjean N. WeP07 

Gregušová D. MoP15 

Greilich A. TuI1 

Grigelionis I. TuP52 

Grodecki K. TuP03, TuP42, 

TuP45 

Gro T. MoP11, MoP28, 

MoP31, MoP40, 

MoP44, MoP45, 

MoP56 

Gryglas-Borysiewicz M. TuP40, 

TuP44, WeP18, 

WeP33 

Grynberg M. TuO1, TuP39, 

TuP46 

Grzanka S. WeO6, WeP19, 

WeP34, WeP38, 

WeP50, WeP55 

Grzegory I. WeO6, WeP07, 

247 

WeP48 

Grzywacz B. WeP19 

Guda K. TuI4 

Gumienny Z. TuP20, TuP35, 

WeP50 

GuziewiczE. MoP12, MoP27, 

WeP06, WeP27, 

WeP30, WeP31, 

WeP41 

Gwarek W. MoO4, TuP46 

H 

Hajduk B. MoP36 

Hałda G. ThI1 

Hankiewicz E.M. MoI3 

Harris J.S. WeP22 

Hartsfield T. TuP12 

Henini M. WeP12 

Henrykowski A. TuP20 

Hey R. TuI4 

Higersberger J. WeP03 

Hilmer H. TuO6 

Hoefling S. TuP16 

Holc K. ThI4 

Hołyst R. MoP51 

Hommel D. SaI1, ThI5, TuO6, 

TuP02, TuP34, 

TuP54, WeP13, 

WeP30 

Hopkinson M. WeP12 

Horvath Z.J. MoP41 

Hosatte M. MoP49 

Hruban A. MoP03, MoP08 

Hrubiak R. MoP04 

Hwang W.S. TuP58 

Ibáñez J. WeP12 

Ievtushenko A.I. MoP41, MoP42, 

MoP43 

Ilaschuk M.I. MoP13 

IlverL. WeP05 

Ivanov S.V. TuP24 

Iwi ska M. MoP20 

Izdebska K. WeP25 

I

_______________________________________________________________ 


J 

Jacak J. TuP20 

Piechota J. WeP54 

Jadczak J. TuP36, TuP43 

Jahn U. WeO4 

Jakieła R. WeO2, WeP31 

Sołtys J. WeP54 

Jakubczyk T. TuO6, TuP02, 

TuP54 

Janicki L. WeP39 

Janik E. MoO5, MoP12, 

MoP51 

Jarimavi i t -Žvalionien R. MoP37 

Jaskolski W. TuP04 

Jaworski D. TuP52 

Jaworski M. WeP27 

Jena D. SuI2, TuP58 

Nygard J. TuP53 

Jie M. MoP18 

Johnson R.L. MoP17, MoP53 

Jong-In S. WeP35 

Jonson M. MoO1 

June K.L. WeP35 

Jungwirth T. WeI1 

Jurkiewicz-Wegner E. MoP08 

Jurusik J. MoP36 

Juszy ski P. WeP18, WeP33 

K 

Kacman P. MoO3, MoP02, 

MoP07 

Kaczmarkiewicz P. TuP11 

Kafar A. WeP23 

Kaim A. WeP46 

Kaminskien Ž. MoP37 

Kami ska A. MoP04, MoP21, 

MoP35, MoP51, 

TuP19 

Kami ska E. MoP16, MoP51 

Kami ska M. MoP03, MoP48, 

WeP20 

Kamyczek P. TuP20, TuP56, 

WeP50 

Karachevtseva L.A. MoP22 

Karbownik P. MoP20 

Karczewski G. MoO5, MoP30, 

MoP57, TuP08, 

TuP13, TuP19, 

TuP20, TuP35 

Karpenko A.Y. MoP42, MoP43 

Karpierz K. TuO1 

248 

Karpyna V.A. MoP23 

Karthikeyan G.S. WeP35 

Karwat P. TuP18 

Katrunov K. MoP29 

Kazimierczuk T. MoO5, TuO4, TuO5, 

TuP02, TuP08, 

TuP09, TuP32 

Ka mierczak P. WeP06 

Keizer J.G. WeP40 

Kempisty P. WeP51, WeP56 

K pisty G. TuP42 

Khachapuridze A. WeP34 

Khomyak V.V. MoP13, MoP25 

Khyzhun O. Yu. MoP25, MoP42 

Kim D. TuI1 

Kirste L. WeP20 

Klochkov L.A. MoP25 

Klochkov L.O. MoP42, MoP43 

Klosek K. WeP02, WeP29, 

WeP57 

Kłopotowski Ł. MoI2, TuP08, 

TuP13, WeP29 

Kłosek K. WeP25 

Knap W. MoO4, ThI6, TuO1, 

TuP37, TuP38, 

TuP41 

Knoff W. MoP02, MoP17, 

MoP32, WeP04 

Koba M. MoP60 

Kobak J. TuP02 

Koenraad P.M. WeP40 

Köhler K. WeP20 

Kolek A. ThI1 

Kolkovsky V. MoP16, MoP30, 

TuP06 

Kolwas K.A. MoP01 

Koperski M. TuP09 

Kopyt P. MoO4, TuP46 

Korbecka A. MoP06 

Korona K.P. MoP48, WeP20 

Korwin-Mikke K. MoP19 

Korzekwa K. TuP15 

Kosiel K. ThI1 

Kossacki P. MoO5, TuO4, TuO5, 

TuP01, TuP02, 

TuP09, TuP54 

Kossut J. TuP13 

Kothleitner G. WeO2 

Kovalyuk Z.D. MoP13, MoP26 

Kowalczyk L. MoP02 

Kowalik I. WeP53 

Kowalik I.A. WeP37 

Kowalski B. MoP25, WeP26 

Kowalski B.J. WeP21, WeP25, 

WeP36

40th _______________________________________________________________ 


Kowalski P. TuP28 

Kozanecki A. MoP04, MoP35, 

MoP46, MoP50 

Koziarskyi D.P. MoP38 

Koziarskyi I.P. MoP38 

Kozłowski A. TuP23 

Kozub M. TuP07, TuP31 

Kozubal M. TuP44 

Krajewski T.A MoP27, WeP30, 

WeP31 

Kret S. MoO5, MoP51 

Krive I.V. MoO1 

Krizhanovskii D. TuI4 

Krogulec I. WeP42 

Krok-Kowalski J. MoP11, MoP28, 

MoP40, MoP44, 

MoP56 

Krukowski S. WeP51, WeP54, 

WeP55, WeP56, 

WeP58 

Kruse C. ThI5, TuO6, TuP02, 

TuP54, WeP13 

Krushynskaya L.A. MoP32 

Kruszewski P. WeP30, WeP31 

Krzy anowska H. WeP49 

Krzy osiak M. TuP10 

Kubisa M. TuP43, TuP49 

Kucharski R. WeP11, WeP39 

Kuchmii S.Ya. MoP22 

Kúdela R. MoP15 

Kudrawiec R. WeP11, WeP12, 

WeP22, WeP35, 

WeP39, WeP47 

Kukli ski K. TuP13 

Kukuła Z. MoP31 

Kümmell T. ThI5 

Kunert G. WeP13 

Kutsay O.M. MoP43 

Ku nicki Z.T. MoP49, ThI9 

Kwiatkowski A. WeP18 

Lapinskas S. MoP37 

Lashkarev G.V. MoP23, MoP25, 

MoP32, MoP41, 

MoP42, MoP43 

Latkowska M. WeP12, WeP22, 

WeP35, WeP47 

Lazorenko V.I. MoP25, MoP32, 

MoP41, MoP42, 

MoP43 

Le V.Kh. WeP14 

Lefebvre P. WeO4 

L 

249 

Leonelli R. WeP16 

Leszczynski M. WeP23, WeP26, 

WeP38 

Marcinkowski L. WeP55 

Levrat J. WeP07 

Li T. WeO2,WeP53 

Li X. TuP12 

Locatelli A. WeP37 

Loeffler A. TuP16 

Loginov D.K. TuP47 

Lopuszynski M. WeP10 

Lucznik B. WeP19, WeP48 

Lukasik P. MoO4 

Luna E. WeO4 

Lytvynenko O.A. MoP22 

Łach P. MoP21, TuP19 

Łaszcz A. MoP19 

Łepkowski S.P. WeO5, WeP08, 

WeP52 

Łuka G. WeP31 

Łukasiewicz M. WeP06 

Łukasiewicz M.I. WeP27 

Łusakowska E. MoP02, WeP02, 

WeP29, WeP31 

Łusakowski A. WeP04 

Łusakowski J. TuO1, TuP30, 

TuP32, TuP37, 

TuP39, TuP46, 

TuP50, TuP51, 

TuP52 

Ł 

M 

Ma C.G. MoP35 

Machnikowski P. TuP07, TuP10, 

TuP11, TuP14, 

TuP15, TuP18, 

TuP25, TuP26, 

TuP28 

Maci ek E. MoP28 

Madrak K. WeP45 

Madsen M.H. TuP53 

Maistruk E.V. MoP38 

Majewski J.A. MoP06, MoP10, 

MoP59, TuO2, 

WeO1, WeO3, 

WeP03, WeP10, 

WeP17 

Majhofer A. WeP45

_______________________________________________________________ 


Malicka E. MoP11, MoP44, 

MoP45, MoP56 

Malkova N. TuP04 

Marcinowski Ł. TuP10 

Marczewski J. TuP37 

D browska-Szata M. TuP56 

Marianchuk P.D. MoP38 

Mariette H. TuP46 

Marinchio H. TuP38 

Marona L. WeP38 

Martinez K.L. TuP53 

Maryanchuk P.D. MoP26 

Marynski A. TuP16 

Materna A. MoP03, MoP08 

Maude D.K. MoO6, MoP24 

M kosa A. MoP30, WeP42 

Meingast A. WeO2 

Meltser B.Y. TuP24 

Meziani Y. TuP38 

Mi Z. WeP16 

Mickevi ius J. MoP29 

Mickievicius S. MoP47, MoP53 

Milowska K. MoP10, TuO2, 

WeO3 

Misiewicz J. TuP11, TuP16, 

TuP31, TuP43, 

TuP49, TuP57, 

WeP11, WeP12, 

WeP22, WeP35, 

WeP39, WeP47 

Mitard J. TuP52 

Molas M. TuP29, TuP30, 

TuP32 

Molenkamp L.W. MoP57 

Monthioux M. MoO1 

Morhange J.F. MoP51 

Mostowski J. TuP10 

Motyka M. WeP11 

Movilla J.L. TuP33 

Mroczy ski R. MoP19 

Mukhin M.S. TuP24 

Musiał A. TuP11, TuP16, 

TuP31 

Muzioł G. WeO6, WeP44 

Mydlarz T. MoP28 

Myers-Ward R.L. TuP58 

N 

Najda S.P. WeP38 

Nakwaski W. MoP52 

Nanishi Y. WeI4 

Narkiewicz U. MoP14 

Navarro-Quezada A. WeO2, WeP37, 

250 

WeP53 

Nawrocki M. TuP02, TuP09, 

WeP53 

Nestoklon M.O. TuP24 

Nguyen H. WeP16 

Nietuby R. WeP21 

Nikiforov K. MoP40 

Niño M.A. WeP37 

Noe L. MoO1 

Nogajewski K. TuO1, TuP46 

Nötzel R. MoO2 

Nouvel P. TuP38 

Novotný T. TuP05 

Nowakowski P. WeP29, WeP57 

Nowicki P. TuP06 

Nygård J. MoO1 

O 

Olender K. MoP30 

Oliveira Jr. N.F. MoP24 

OnurMente T. WeP37 

Orlita M. MoO6 

Orłowski B.A. MoP17, MoP47, 

MoP53 

Orłowski W. MoP08 

Ott F. WeP24 

Pacuski W. TuO6, TuP02, 

TuP54, WeP06, 

WeP53 

Pacyna A.W. MoP11, MoP28, 

MoP40, MoP56 

Papierska J. WeP06, WeP53 

Papis E. TuP50 

Parfenyuk O.A. MoP13 

Pasternak J. MoP19, MoP51 

Pawlowski M. WeP14 

Pawłowska J. WeO6 

Pełech I. MoP14 

Peres M.L. MoP24 

Perlin P. ThI4, WeO6, 

WeP23, WeP26, 

WeP34, WeP38 

Petrouchik A. MoO5 

Pi M. TuP33 

Piersa M. MoP03, MoP08 

Pier ci ska D. MoP20 

Pier ci ski K. MoP20 

Pietnoczka A. MoP18 

P

40th _______________________________________________________________ 


Pietrzyk M.A. MoP17, MoP46, 

MoP50, MoP53 

Pi tka B. TuP50, TuP51 

Piot B.A. MoO6 

Piotrowska A. MoP16, MoP19 

Piotrzkowski R. WeP34 

Placzek-Popko E. TuP56 

Planelles J. TuP33 

Plaziak J. WeP03 

Plochocka P. TuO4 

Pochrybniak C. WeP43 

Pociecha D. WeP45 

Podemski P. TuP11, TuP16 

Popko E. TuP20, TuP35, 

WeP50 

Potemski M. MoO6, TuO4, TuP36 

Proselkov O. TuO3, WeP15 

Prosy evas I. MoP37 

Przezdziecka E. MoP04, MoP46, 

MoP50 

Przybytek J. TuP40, TuP44, 

WeP18, WeP33 

Ptasi ska M. WeP54 

Pyszniak K. TuP55 

R 

Radchenko M.V. MoP32 

Radzvilavicius A. MoP05 

Rancova O. TuP27 

Rappl P.H. MoP24 

Ratchford D. TuP12 

Rawski M. TuP55 

Rduch P. MoP40, MoP44, 

MoP45 

Reithmaier J.P. TuP16, TuP31 

Reitzenstein S. TuP16 

Reszka A. MoP02, MoP25, 

MoP47, MoP53, 

TuP19, WeP02, 

WeP25, WeP26, 

WeP36 

Reuter D. TuP57 

Romaniec M. MoP08 

Roshko V.Ya. TuP48 

Rossbach G. WeP07 

Roszak K. TuP05, TuP10 

Rousset J.-G. WeP53 

Rovezzi M. WeO2, WeP37 

Ró a ski P.T. MoP09 

Rudzi ski M. WeP39 

Ryczko K. TuP57 

Ryzhikov V. MoP29 

251 

Sadowski J. TuO3, WeP05, 

WeP15, WeP18, 

WeP21, WeP24, 

WeP28, WeP33, 

WeP36, WeP42, 

WeP49 

Sajkowski J.M. MoP46, MoP50 

Sakowicz M. WeP16 

Sakowski K. WeP55, WeP56 

Sanchez-García M.A. WeO4 

Sankowski P. MoP07 

Santos P.V. TuI4 

Sarker D. TuI4 

Sarmiento T. WeP22 

Sarzynski M. WeP26 

Sawicka M. WeO6, WeP19 

Sawicki M. TuO3, WeO2, 

WeP06, WeP15, 

WeP53 

Š epka T. MoP15 

Schillak P. TuP17 

Schmidt-Grund R. TuO6 

Schneider J.M. MoO6 

Schreyeck S. MoP57 

Schumacher C. MoP57 

Schuster F. MoO4 

Sciesiek M. TuP54 

Seabaugh A. TuP58 

Semenov A.N. TuP24 

S k G. MoI4, TuP11, 

TTuP16, uP31, 

WeP12 

Sheikin I. MoO6 

Shekhter R.I. MoO1 

Shevchenko D. MoP29 

Shtepliuk I.I. MoP25 

Shur M.S. TuO1 

Sibera D. MoP14 

Sichkovskyi V.I. MoP32 

Siekacz M. WeO6, WeP19, 

WeP44 

Sildos I. MoP21 

Silva C. WeP16 

Simoen E. TuP52 

Sims J. TuP04 

Sitarek P. TuP57 

Sitek A. TuP18 

Sitko R. MoP44 

Sitnikova A.A. TuP24 

Sitek A. TuP14 

Siusys A. WeP36 

Sizov F.F. MoP22 

S

_______________________________________________________________ 


Skierbiszewski C. WeO6, WeP19, 

WeP44 

Skolnick M.S. TuI4 

Skowro ski W. ThI7 

Słupi ski T. MoP18 

Smajek E. MoP02 

Smakman E.P. WeP40 

Smole ski T. TuP01 

Smrcka L. MoO6 

Soba ska M. WeP02, WeP25, 

WeP29, WeP57 

Sochacki M. MoP19, TuP45 

Solignac P. TuP41 

Sorensen C.B. TuP53 

Spałek J. TuP22 

Speck J.S. WeI3 

Springholz G. MoP01 

Stachowicz M. MoP46, MoP50 

Stallinga P. WeP30 

Sta czyk S. WeP23 

Starik S.P. MoP43 

Starzhinskiy N. MoP29 

Staszczak G. WeP34 

Stefanowicz W. TuO3, WeO2, 

WeP06, WeP15, 

WeP53 

Stelmakh Y.A. MoP32 

St pniewski R. TuP03, TuP42, 

TuP44, TuP45 

Stobiecki T. ThI7 

Story T. MoP02, MoP17, 

MoP32, MoP57, 

WeP04 

Strak P. WeP51, WeP56, 

WeP58 

Stronska O.J. MoP22 

Stroyuk A.L. MoP22 

Strupi ski W. TuP03, TuP42, 

TuP44, TuP45, 

WeP39 

Strzelecka G. MoP03, MoP08 

Suchocki A. MoP04, MoP21, 

MoP35, TuP19, 

WeP25 

Suffczy ski J. TuP02, WeP06, 

WeP53 

Suski T. WeP07, WeP23, 

WeP26, WeP34, 

WeP38, WeP50 

Svoboda P. MoO6 

Swiatek K. WeP14 

Sybilski P. WeP25 

Syperek M. TuP43, WeP22, 

WeP35 

Szczepa ski P. MoP60 

252 

Szczerbakow A. MoP53 

Szczytko J. TuP50, TuP51, 

WeP43, WeP45, 

WeP46 

Szerling A. MoP20, ThI1 

Sznajder M. MoP33 

Sznajder P. TuP51 

Szot M. MoP02, MoP57 

Sztenkiel D. WeO2, WeP09 

Szuszkiewicz W. MoP51, WeP24 

Szydlowska J. WeP46 

Szymura M. TuP08 

liwa C. WeO3, WeP01 

T 

Tahy K. TuP58 

Taliashvili B. MoP02, MoP17 

Tamulaitis G. MoP29 

Tang Z. TuP12 

Taube A. MoP19 

Tedesco J.L. TuP58 

Teisseyre H. MoP04, WeP07, 

WeP29, WeP48, 

WeP52 

Teppe F. MoO4, ThI6, TuP37, 

TuP38, TuP41 

Thiess S. MoP47 

Timofeeva I.I. MoP25 

Tkach V.M. MoP42 

Tkaczyk Z. WeP42 

Tomaszewicz E. MoP31 

Tomaszewski D. TuP37 

Toropov A.A. TuP24 

Torres J. TuP38, TuP41 

Trampert A. WeO4 

Trushkin S. MoP01 

Trzeciakowski W. WeP17 

Turek M. TuP55 

Turski H. WeO6, WeP19, 

WeP44 

Twardowski A. WeP43, WeP45, 

WeP46 

U 

Ueta A.Y. MoP24 

Ulfat I. WeP05 

Ulin V.P. MoP55 

Umansky V. TuP39 

Urbanowicz P. MoP31 

Urba czyk A. MoO2

40th _______________________________________________________________ 


Utko P. MoO1,TuP53 

V 

vanOtten F.W.M. MoO2 

vanVoornveld R. WeP40 

Varani L. TuP38 

Vasek P. MoO6 

Videlier H. TuP37 

Vincent B. TuP52 

Vyborny Z. MoO6 

W 

Wachnicki Ł. MoP12, MoP27, 

WeP30, WeP31, 

WeP41 

Walukiewicz W. ThI2 

Wasik D. WeP18, WeP33 

Wasilewski Z. WeO6 

Wasilewski Z.R. TuP29, TuP41 

Wei S.H. MoP18 

Welna M. WeP11 

WernerZ. WeP43 

Weszka J. MoP36, MoP54 

Wiater M. MoP02, MoP51, 

TuP06 

Wieck A. TuP57 

Wierzbicka A. MoP46, MoP50, 

WeP02, WeP29 

Wilamowski Z. MoP03, WeP27 

Winkler T.E. WeO2 

Wisniewski P. WeP38 

Wi niewski P. WeP23 

Wi niewski Z. WeP25 

Witkowski B. WeP57 

Witkowski B.S. MoP12, MoP14, 

MoP27, MoP49, 

WeP31, WeP41 

Witowski A.M. WeP06 

Wittlin A. WeP27 

Władarz G. MoP40 

Woi ska M. WeP45 

Wojciechowski T. TuP13 

Wojnar P. MoO5, TuO4, TuO5, 

TuP08, TuP09, 

TuP13, TuP19 

253 

Wojtowicz T. MoO5, MoP02, 

MoP51, TuP06, 

TuP08, TuP13, 

TuP19, TuP30, 

TuP32, TuP46 

Woło A. MoP03 

Wolska E.A. MoP14 

Woło A. WeP27 

Wosi ski T. MoP30, WeP28, 

WeP42, WeP49 

Wouters M. TuI4 

Wójs A. TuI3, TuP36 

Wrachtrup J. MoI1 

Wróbel J. TuP06, TuP39, 

WeP42 

Wu S.H. MoP48 

Wysmołek A. TuP03, TuP42, 

TuP44, TuP45 

X 

Xing H. TuP58 

Yakovlev D.R. TuP36 

Yamaguchi T. WeI4 

Yang J. TuO1 

Yaremko A.M. MoP23 

Yastrubchak O. WeP28, WeP49 

Yatsunenko S.A. MoP14 

Yoon E. WeI4 

Yurtsenyuk N.S. MoP39 

Zaj c M. WeP11, WeP39 

Zakrzewski A.J. WeP31 

Zakrzewski T. WeP32 

Zaleszczyk W. MoP51 

Zału ny M. TuP23 

Zapalska M. MoP58 

Zdrojek M. MoP19 

Zhang S. WeP16 

Zholudev M. TuP41 

Zieli ski M. MoP09, TuP04 

Zielony E. TuP20, TuP35, 

WeP30, WeP50 

Ziółkowska D. MoP48 

Y 

Z

_______________________________________________________________ 


Zürbig V. TuP31 

Zychowska M. MoP19 

ak D. MoP52 

uberek R. WeP15 

ytkiewicz Z.R. MoP04, WeP02, 

WeP25, WeP29, 

WeP57, WeP58 

uk J. TuP55, WeP28, 

WeP49 

254

____________________ NOTES ____________________

____________________ NOTES ____________________

____________________ NOTES ____________________

____________________ NOTES ____________________

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Addendum to the Book of Abstracts 

� 

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