Deutsche Tagung f ¨ur Forschung mit ... - SNI-Portal

Nanostrukturen und Grenzflächen Poster: Do., 13:00–15:30 D-P282
Controlling Planar and Vertical Ordering in Three-Dimensional (In,Ga)As
Quantum Dot Lattices by GaAs Surface Orientation
Daniil Grigoriev 1 , Martin Schmidbauer 2 , Shahram Seydmohamadi 3 , Zhiming
Wang 3 , Yuri Mazur 3 , Gregory Salamo 3 , Peter Schäfer 1 , Michael Hanke 4 ,
Rolf Köhler 1
1 Institut fur Physik, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany –
2 Institut für Kristallzüchtung, D-12489 Berlin, Germany – 3 Department of Physics,
University of Arkansas, Fayetteville, Arkansas, 72701, USA – 4 Martin-Luther-
Universität Halle-Wittenberg, D-06120 Halle/Saale, Germany
The process of self-organized growth of quantum dots (QD) in Stranski-Krastanow
mode is affected not only by elastic properties of the substrate material, but also
by physical properties of the surface. Thus, for GaAs (100) surface, due to the 2x4
reconstruction oriented along (01-1) direction the diffusion length in this direction
is higher than for the elastically equal (011) direction. As a result, in the case of
multilayer InGaAs QD structures under the certain growth conditions [1,2], QD are
arranged in chains in (01-1) direction, demonstrating an excellent vertical correlation
as well. The diffusion length, and so the type of ordering, could be effectively controlled
by introducing the surface steps perpendicular to (01-1) direction, or, in other words,
introducing so-called high-index surfaces with controlled miscut towards the (01-1) insurface
direction. The surface steps on these surfaces play the role of potential barriers
for the material transfer.
In order to probe the 3D ordering of QD lattices x-ray diffuse scattering has been
monitored three-dimensionally by a special multi-detection technique using a CCD
detector [3]. The experiments have been carried out on beamlines W1 and BW2 at
HASYLAB/DESY. The surfaces under investigation are GaAs (100) and GaAs (n11)B,
where n is equal to 9, 7, 5, 4 and 3. The high index surfaces are tilted towards (111)B
surface which forms B-type steps running along [011]-direction.
In the talk we will demonstrate that all the samples under investigation show a complex
3D regular QD structure. Vertical ordering is mainly stress-determined, and the angle
of the vertical inheritance varies non-monotonically between two limiting cases of (100)
and (111)B surface orientation. Pplanar QD ordering is essentially determined by the
surface anisotropy of material-transfer. We may contend that the planar ordering
evolves from a linear one for (100) surface to an almost rectangular one for the (911)B
surface through the set of rhombic- like unit cells and the angle of the rhombus opening
angle θ, which depends linearly on the surface step density. The best regularity of the
QD structure have been established for the (411)B surface. All the above-mentioned
opens the way for controlled processing of highly ordered 3D QD structures with known
parameters.
[1] Wang et al., Appl.Phys. Lett. 84 (2004) 1931
[2] Yu. I. Mazur et al., Appl. Phys. Lett. 83, 987 (2003).
[3] D Grigoriev et al., J. Phys. D: Appl. Phys. 38 (2005) A154A159