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5.7 Summary Figure 5.7: Schematic band diagram of the transition region between the crystalline and disordered phase in µc-Si:H. band diagram as shown in Fig. 5.7 can be drawn. The results support an earlier suggestion that in µc-Si:H there should exist a considerable conduction band offset between the crystalline regions (for which the crystalline silicon band gap E G = 1.1 eV is assumed) and the disordered regions (for which the a-Si:H gap E G = 1.8 eV is assumed [65]). This would result in a significant overlap between the energy of DB and CE center as shown in Fig. 5.7. Otherwise the simultaneous occurrence of the CE and the DB signal for significant E F shifts are difficult to explain if one does not allow for strong potential fluctuations in the material. Apparently, this earlier assumption concluded from dark and light induced ESR studies on highly crystalline material is valid even in material with very small crystalline volume fraction [30]. Even for material with IC RS = 0.08 containing only a minute amount of the crystalline phase, i.e., crystalline grains strongly diluted in the amorphous matrix, doping concentration as low as 5×10 16 cm −3 can shift the Fermi level into the conduction band-tail of the crystallites and activate a stable CE resonance. 5.7 Summary The doping induced Fermi level shift in µc-Si:H, for a wide range of structural compositions, is governed by the compensation of defect states for doping concentrations up to the dangling bond spin density. For higher doping concentrations a doping efficiency close to unity is found. The close relationship between the CE resonance intensity and the conductivity is confirmed, which means the elec- 61
Chapter 5: N-Type Doped µc-Si:H trons contributing to the CE signal represent the majority of the charge carriers contributing to electric transport. The fact, that for low defect material the N CE approaches the value of the maximum doping concentration, proves the close relation between phosphorus concentration N P and N CE . However, while in earlier investigations a built-in factor of 0.5 and a doping efficiency of unity was found the results presented here suggest that both are of the order of unity, assuming that charge transfer from the amorphous phase can be excluded. Measuring the real phosphorous concentration using high resolution ion mass spectroscopy (SIMS) 1 could resolve this puzzle and will be a task for future experiments. A significant conduction band off-set between crystalline and disordered regions in µc-Si:H is suggested in agreement with earlier studies. 1 Note, that the sensitivity limit of a quadrupole mass spectrometer for the measurement of P- concentrations exceeds several 10 18 cm −3 , due to the presence of silicon hydrides of nearly the same mass as the phosphorous ions. Using a high resolution mass spectrometer, the mass defect between 31 P and the different silicon hydrides can be used to discriminate between the respective ions. 62
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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
Page 24 and 25: 2.2 Electronic Density of States ta
Page 26 and 27: 2.2 Electronic Density of States Fi
Page 28 and 29: 2.3 Charge Carrier Transport influe
Page 30 and 31: 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 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(
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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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