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5.4 Dangling Bond Density Figure 5.3: ESR spectra of samples with crystallinities of IC RS ≈0.82, 0.72, 0.47, 0.08, and 0 with gas phase doping concentrations of PC =1, 5, and 10 ppm measured at T=40K. The vertical dotted lines indicate the position of db 1 ,db 2 , and CE resonances at values of g=2.0043, g=2.0052, and g=1.996-1.998, respectively, typically found in µc-Si:H. with increasing doping level PC. In addition to the CE signal, the DB signal (db 1 +db 2 ) is visible in all samples, although in the case in which the CE line is most dominating (e.g. IC RS = 0.77 and with PC = 10 ppm) the DB signal is at the lower limit for a multi-peak de-convolution analysis to be feasible. Doping induced effects can be observed in all spectra of material where a crystalline phase can be observed (IC RS > 0). The existence of the resonance at g=1.996-1.998 is a direct result of a shift of E F up into the conduction band- tail. With increasing doping concentration, more and more states in the conduction band-tail are getting occupied and contribute to the intensity of the resonance. The shift of the Fermi level, however, is governed by the compensation of gap states. For a fixed doping concentration, the high defect density in the IC RS ≈ 0.82 material leads to a considerable lower CE spin density N CE compared to the low defect material IC RS ≈ 0.77 and 0.47. It is quite surprising, that even for material with crystalline grains that are highly diluted in an amorphous phase (IC RS ≈ 0.08) a strong CE line can be observed. 5.4 Dangling Bond Density To obtain the spin density of each superimposed line shown in Fig. 5.3, a numerical fitting procedure was applied. The DB-signals at g=2.0043 and g=2.0052 could be well approximated by Gaussian lines. For the CE line at g=1.996−1.998 a convolution of a Gaussian and Lorentzian curve was used. However, a separa- 55
Chapter 5: N-Type Doped µc-Si:H Figure 5.4: Dangling bond spin density versus IC RS obtained from numerical fitting of the ESR line shown in Fig. 5.3 (a) vs. the Raman intensity ratio IC RS and (b) vs. the gas phase doping concentration PC . tion of the two DB signals is impossible from the spectra shown above; therefore only the sum of both will be analyzed in this section. Fig. 5.4 (a) shows the dangling bond (DB) density obtained from this deconvolution procedure versus the Raman intensity ratio IC RS . Additionally, the DB density N DB for the undoped material is shown. As already shown in Chapter 4 for the intrinsic material, the DB density N DB decreases with increasing amorphous phase contribution. In principle one can observe the decrease of N DB upon decreasing IC RS for all doping concentrations, but with increasing doping level this phenomena is less pronounced. It is surprising indeed that even for the highest doping concentrations of PC = 10 ppm, DB states can still be observed in all samples. However, depending on the crystallinity there are some distinct differences in how the dangling bond density N DB changes as a function of PC. This is shown in Fig. 5.4 (b), where the spin density is plotted versus the gas phase doping concentration. For the highly crystalline sample (IC RS = 0.82) the spin density decreases steeply from 0 ppm to 1 ppm and stays almost constant at N DB ≈ 10 16 cm −3 for higher doping concentrations. For the highly crystalline samples (IC RS = 0.77−0.47) the spin density stays almost constant or slightly decreases from already low values of N DB = 1×10 16 cm −3 for PC=0 ppm to N DB = 6×10 15 cm −3 for PC=10 ppm. This is a result of compensation. For samples with an even higher amorphous phase contribution (IC RS < 0.10), an increasing dangling bond density can be observed. It seems unlikely that the reason for the increasing N DB is caused by the doping induced dangling bond creation, known from hydrogenated amorphous silicon [89, 90], because these states can not be observed in ESR. It is more plausible that within the investigated doping range, the occupation 56
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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
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
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 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
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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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