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6.1 Metastable Effects in µc-Si:H Figure 6.5: Spin density of the resonances at g=2.0043 and g=2.0052 before and after treatment in H 2 O. db 2 line increases by more than a factor of 6 from values of N S = 8 × 10 15 cm −3 to N S = 5 × 10 16 cm −3 while the db 1 resonance remains constant at values of about N S = 1.5 × 10 16 cm −3 . As expected from the overall spin density plotted in Fig. 6.3 (b) the absolute changes decrease with increasing amorphous content, the characteristic, however, remains the same. The line analysis shows that the increasing spin density can be attributed to an increase of the db 2 resonance while the db 1 resonance at g=2.0043 stays constant. In this section, it has been reported that the spin density of µc-Si:H increases as a result of contact with atmospheric gases or by a treatment in H 2 O. In particular, the number of spin states contributing to the db 2 resonance increases, while the spins of db 1 remain unaffected. The magnitude of the instability changes thus depends strongly on the particular structure. With increasing amorphous content and more compact structure the changes are reduced or may even disappear. However, so far the reason for these changes and the particular processes involved are unclear. It is interesting to consider if, and how, the material can be returned back to its initial state. The clear dependency of the magnitude of the changes in N S on the structure, in particular the porosity, suggests that surface processes are involved. Assuming that the changes in the ESR signal intensity are a result of adsorption of atmospheric gases or water, annealing in inert gas atmosphere or vacuum might restore the initial material properties. This is the subject of the 69
Chapter 6: Reversible and Irreversible Effects in µc-Si:H Figure 6.6: ESR signals of highly crystalline porous (IC RS = 0.82), highly crystalline compact (IC RS = 0.71), and from material at the transition from crystalline to amorphous growth = 0.47 for different annealing periods.) (I RS C following section. 6.1.2 Reversible Effects in the ESR Signal Material as studied above, i.e. with structure compositions including highly crystalline porous, highly crystalline compact, and transition material with a considerable amount of a-Si:H phase, has been stored in air for a prolonged period and afterwards sealed into argon atmosphere. The samples were then annealed at a temperature of 80 ◦ C for several hours. At regular intervals the annealing process was interrupted in order to measure ESR. The resulting spectra are plotted in Fig. 6.6. Unlike the ESR measurements shown before, these spectra are not normalized to the same peak height, but relative to the initial curve, denoted as (1.). Again the vertical lines indicate the position of the g-values at g=2.0043 and g=2.0052. The most outstanding result in Fig. 6.6 is that quite moderate annealing temperatures of T = 80 ◦ C strongly influence the ESR signal. As expected from the instabilities observed above, the magnitude of the effects is closely connected to the structure of the material. Significant changes can be observed for the highly crystalline porous material (IC RS = 0.82). The ESR signal decreases strongly after one hour annealing in argon atmosphere. With increasing annealing period t ann the signal intensity decreases further. On the other hand, the ESR signal of the highly crystalline compact material (IC RS = 0.71) changes only slightly. This is quite surprising as instability effects could also be observed for these types of 70
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Forschungszentrum Jülich in der He
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Forschungszentrum Jülich GmbH Inst
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Kurzfassung In der vorliegenden Arb
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Abstract The electronic properties
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Contents 1 Introduction 1 2 Fundame
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CONTENTS C Abbreviations, Physical
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Chapter 1 Introduction Solar cells
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defect states provided that they ar
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Chapter 8: In this chapter, the inf
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Chapter 2 Fundamentals In this firs
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2.2 Electronic Density of States St
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2.2 Electronic Density of States ta
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2.2 Electronic Density of States Fi
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2.3 Charge Carrier Transport influe
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2.3 Charge Carrier Transport functi
Page 32 and 33: Chapter 3 Sample Preparation and Ch
Page 34 and 35: 3.1 Characterization Methods Figure
Page 36 and 37: 3.1 Characterization Methods Homoge
Page 38 and 39: 3.1 Characterization Methods µ Fig
Page 40 and 41: 3.1 Characterization Methods compar
Page 42 and 43: 3.1 Characterization Methods bution
Page 44 and 45: 3.1 Characterization Methods posite
Page 46 and 47: 3.2 Deposition Technique admixture
Page 48 and 49: 3.3 Sample Preparation 3.3.1 Sample
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
Page 58 and 59: 4.3 ESR Signals and Paramagnetic St
Page 60 and 61: 4.4 Discussion - Relation between E
Page 62 and 63: 4.4 Discussion - Relation between E
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
Page 98 and 99: Chapter 7 Transient Photocurrent Me
Page 100 and 101: 7.2 Transient Photocurrent Measurem
Page 106 and 107: 7.3 Temperature Dependent Drift Mob
Page 108 and 109: 7.4 Multiple Trapping in Exponentia
Page 110 and 111: 7.5 Discussion Table 7.2: Multiple
Page 112 and 113: 7.5 Discussion 7.5.3 The Meaning of
Page 114 and 115: Chapter 8 Schematic Density of Stat
Page 116 and 117: silicon as shown in Fig. 8.1 b, whi
Page 118 and 119: Chapter 9 Summary In the present wo
Page 120 and 121: Appendix A Algebraic Description of
Page 122 and 123: Eq. A.7 then becomes L(t) F = sin(
Page 124 and 125: Appendix B List of Samples Table B.
Page 126 and 127: Table B.3: Parameters of n-type µc
Page 128 and 129: Appendix C Abbreviations, Physical
Page 130 and 131: 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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