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5.5 Conduction Band-Tail States Figure 5.5: (a) Spin density of the CE resonance (N CE ) in the doped samples and the DB resonance (N CE ) in undoped material; (b) CE intensity of the microcrystalline phase as a function of conductivity. of D + states by an electron creating an D 0 state exceeds the compensation of D 0 states. This would be the case if in the undoped state the mean energy position of the defect is above E F . Material prepared at yet higher doping concentration could give additional proof for this thesis. The dangling bond signal can be detected in all spectra for all gas phase doping concentrations investigated. Within the highly crystalline regime, N DB decreases between PC = 0 ppm and 1 ppm, but stays almost constant for higher doping concentrations. 5.5 Conduction Band-Tail States The deconvolution into the individual lines can also be used to determine the number of paramagnetic states in the conduction band-tail. The results for the calculated CE spin density N CE for different doping levels are shown in Fig. 5.5 (a) as a function of IC RS . Additionally, the dangling bond densities N DB for undoped material are plotted in the graph. The variation of N CE as a function of IC RS and PC follows nicely the same qualitative behavior as the conductivity plotted in Fig. 5.2 (a). This confirms earlier studies on n-doped highly crystalline material [35, 39]. As expected, the intensity of the CE signal seems to be moderated by the dangling bond density. Material exhibiting the highest crystallinity IC RS = 0.82 and also the highest N DB shows lower CE line intensity compared to the IC RS = 0.72 and IC RS = 0.47 material, where lower N DB are observed. For samples with a crystalline volume fraction lower than IC RS = 0.47 the influence of N DB on doping is masked by effects of the structural change. ESR as an integrating measurement 57
Chapter 5: N-Type Doped µc-Si:H Figure 5.6: Normalized CE spin densities N CE(norm) as a function of the Raman intensity ratio IC RS . Also indicated are the maximum doping concentrations evaluated from the gas phase doping concentrations PC using a built-in factor and a doping efficiency of one. technique measures the number of spins in a particular amount of material. Because the CE resonance only originates from the crystalline phase, one would expect that the density decreases with increasing amorphous content. This can be seen for the low level doped samples, where the spin density N CE decreases by about one order of magnitude with decreasing crystallinity from IC RS = 0.47 to 0.08. Fig. 5.5 (b) shows N CE against the gas phase doping concentration. For the crystalline low defect material (IC RS = 0.72 − 0.47) N CE increases nearly linearly with a structure independent slope as a function of increasing gas phase doping concentration. On the other hand, the influence of the high dangling bond density N DB = 7.2 × 10 16 cm −3 (for IC RS = 0.82 material) and the low crystalline volume fraction (IC RS = 0.08) results in lower CE intensities. For higher doping concentrations these effects are less pronounced and result in higher CE spin densities. To account for the fact that the CE signal originates only from the crystalline phase of the µc-Si:H material, the CE spin densities N CE were normalized with respect to the crystalline volume content IC RS . The results are plotted in Fig. 5.6. Also indicated in Fig. 5.6 are the maximum dopant densities calculated with a built-in factor of one and a doping efficiency of unity, taken with respect to the atomic density of silicon of 5×10 22 cm −3 . For example, PC = 1 ppm corresponds to a donor density of 5 × 10 16 cm −3 . Apparently, with this simple normalization procedure, the influence of the structural change on N CE (Fig. 5.5 (a)) can completely be compensated. Independent of the structure composition, N CE(norm) increases as a function of the doping concentration. On the other hand, N CE(norm) increases with decreasing IC RS , saturating at the value of the maximum doping 58
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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
Page 20 and 21: Chapter 2 Fundamentals In this firs
Page 22 and 23: 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 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
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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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