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3.3 Sample Preparation 3.3.1 Sample Preparation for ESR and conductivity measurements For ESR measurements the use of powdered samples allows large amounts of material to be placed in the resonant cavity. This results in high signal intensities and thereby an improved signal-to-noise ratio. Therefore, material investigated by ESR, is usually deposited on aluminum (Al) foil. For the deposition standard household foil (brand ”Alio”) was cleaned with 2-Propanol (99.5% purity) and wrapped around four glass substrates, each of 25 × 100 mm 2 size. Usually one of the substrates was equipped with one or two square holes (10 × 10 mm 2 )in which a different substrate could be placed, e.g. roughened glass substrates for conductivity measurements. A typical arrangement of the substrates is shown in Fig. 3.5. After deposition the chamber was flushed with argon for 5 minutes and then evacuated. To cool down, the substrate was kept in vacuum (p ≈ 10 −9 mbar) for at least 3 hours. Afterwards, the material was immediately prepared for the measurement. The Al foil was etched away with a 16% HCl solution. The remaining flakes of µc-Si:H material were filtered out and thoroughly rinsed in de-ionized water. Finally the material was dried for about 24 hours at ambient (T ≈ 30 ◦ C). The µc-Si:H powder was then inserted into quartz tubes with an inner diameter of 4 mm and a wall thickness of d = 0.5 mm. If the powder consisted of very loosely packed flakes, which was the case for highly crystalline films, the material was additionally crushed to obtain comparable packing densities and filling heights. Figure 3.5: Typical substrate arrangement for the deposition of µc-Si:H thin films using Al foil. The Al foil is wrapped around 4 glass substrates (25 × 100 mm 2 ). The square holes in one of the substrates were used to mount roughened glass substrates, which were co-deposited and later used for e.g conductivity measurements. 35
Chapter 3: Sample Preparation and Characterization µ µ Figure 3.6: Schematic picture of a pin diode prepared for time-of-flight measurements. This procedure also made sure that the material fits into the homogeneous part of the magnetic field. To maintain a defined environment, the powdered material was sealed into the quartz tubes under He atmosphere. This procedure yielded filling heights of about 0.5 − 1 cm with a material mass between 22 − 300 mg. During this process the µc-Si:H is in contact with water and air for several hours. Alternatively, material has been also deposited on molybdenum foil (Mo). The foil had a size of 100 × 100 mm, a thickness of d = 0.05 mm, and a purity of 99.9%. From the Mo foil the material peeled off in flakes after bending the foil and could be sealed immediately without further treatment. As for the Al substrates, the Mo foil was equipped with a hole so that e.g. glass substrates could be deposited in the same run. To study the influence of different environments during storing or annealing, the material was removed from the He filled tubes and sealed into Ar or O 2 atmosphere or was treated in HCl solution or water as discussed above. Samples for conductivity measurements have been prepared on roughened borosilicate glass (4 × 15 mm 2 ) in the same run as their ESR counterparts. Roughened glass was used because films with a thickness larger than d =1 µm tend to peel off from a smooth substrate. After deposition, coplanar silver contacts were evaporated under high vacuum conditions having a thickness of 700 nm, a width of 4 mm, and a distance of 0.5 mm. 3.3.2 PIN-Diodes for Transient Photocurrent <strong>Measurements</strong> Besides limitations due to the material investigated, the main criterion for a specimen suitable for time-of-flight (TOF) measurements is the existence of blocking contacts. The samples used for time-of-flight measurements were pin structures as shown in Fig. 3.6 which were prepared using VHF-PECVD (for details about the process see section 3.2.1). As in forward bias the pin diode passes the current, in 36
Page 1 and 2: Forschungszentrum Jülich in der He
Page 4 and 5: Forschungszentrum Jülich GmbH Inst
Page 6 and 7: Kurzfassung In der vorliegenden Arb
Page 8 and 9: Abstract The electronic properties
Page 10 and 11: Contents 1 Introduction 1 2 Fundame
Page 12 and 13: CONTENTS C Abbreviations, Physical
Page 14 and 15: Chapter 1 Introduction Solar cells
Page 16 and 17: defect states provided that they ar
Page 18 and 19: Chapter 8: In this chapter, the inf
Page 20 and 21: Chapter 2 Fundamentals In this firs
Page 22 and 23: 2.2 Electronic Density of States St
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Page 46 and 47: 3.2 Deposition Technique admixture
Page 50 and 51: 3.3 Sample Preparation reverse bias
Page 52 and 53: Chapter 4 Intrinsic Microcrystallin
Page 54 and 55: 4.2 Electrical Conductivity Figure
Page 56 and 57: 4.3 ESR Signals and Paramagnetic St
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Page 60 and 61: 4.4 Discussion - Relation between E
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Page 64 and 65: Chapter 5 N-Type Doped µc-Si:H In
Page 66 and 67: 5.2 Electrical Conductivity Figure
Page 68 and 69: 5.4 Dangling Bond Density Figure 5.
Page 70 and 71: 5.5 Conduction Band-Tail States Fig
Page 72 and 73: 5.6 Discussion concentration evalua
Page 74 and 75: 5.7 Summary Figure 5.7: Schematic b
Page 76 and 77: Chapter 6 Reversible and Irreversib
Page 78 and 79: 6.1 Metastable Effects in µc-Si:H
Page 88 and 89: 6.2 Irreversible Oxidation Effects
Page 94 and 95: 6.3 On the Origin of Instability Ef
Page 96 and 97: 6.3 On the Origin of Instability Ef
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Chapter 7 Transient Photocurrent Me
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7.2 Transient Photocurrent Measurem
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7.3 Temperature Dependent Drift Mob
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7.4 Multiple Trapping in Exponentia
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7.5 Discussion Table 7.2: Multiple
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7.5 Discussion 7.5.3 The Meaning of
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Chapter 8 Schematic Density of Stat
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silicon as shown in Fig. 8.1 b, whi
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Chapter 9 Summary In the present wo
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Appendix A Algebraic Description of
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Eq. A.7 then becomes L(t) F = sin(
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Appendix B List of Samples Table B.
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Table B.3: Parameters of n-type µc
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Appendix C Abbreviations, Physical
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µ d Drift mobility µ d,h Hole dri
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Bibliography [1] E. Becquerel. Mém
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BIBLIOGRAPHY [21] D. Will, C. Lerne
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BIBLIOGRAPHY [45] H. Overhof and M.
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BIBLIOGRAPHY [66] P.W. Anderson. Ab
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BIBLIOGRAPHY [93] J.W. Orton and M.
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BIBLIOGRAPHY [121] J.R. Haynes and
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BIBLIOGRAPHY [148] W. Luft and Y.S.
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BIBLIOGRAPHY [170] G.N. Advani, R.
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List of Publications 1. T. Dylla, R
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Acknowledgments At this point, I wa
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Schriften des Forschungszentrums J
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Forschungszentrum Jülich in der He
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