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6.2 Irreversible Oxidation Effects ≈ ≈ ≈ Figure 6.10: ESR signals of highly crystalline and porous (IC RS = 0.81), highly crystalline compact (IC RS = 0.72), and of material at the transition from crystalline to amorphous growth (IC RS = 0.47) reversible effects in σ D show many similarities to earlier investigations made on material which was grown using the chemical transport technique [20] or hot wire chemical vapor deposition [166]. 6.2 Irreversible Oxidation Effects As shown above, storing highly crystalline µc-Si:H in air atmosphere results in a reversible increase of the spin density accompanied by a shift of the average g-value. However, it has been shown by e.g. infrared spectroscopy, that highly crystalline µc-Si:H is also susceptible to oxidation effects [11, 20, 51, 13], forming Si-O bonds at the grain boundaries, which are stable up to temperatures of T = 1050 K [20]. In the following section, effects of the oxidation of the grainor column boundaries on the ESR signal will be studied. Therefore, samples with different structure compositions, in fact material prepared in the same run as the one used for the air-exposure/annealing cycles (section 6.1), have been sealed into oxygen atmosphere and annealed at temperatures of T = 80 ◦ C. After selected time intervals the annealing process was interrupted and ESR spectra were recorded. The spectra measured for the three structure compositions are shown in Fig. 6.10. As for the reversible changes discussed above, the magnitude of the observed changes strongly depends on the structure composition of the µc-Si:H. However, in contrast to the treatment in argon, annealing in oxygen atmosphere at a temperature of T = 80 ◦ C leads to an increase of the ESR signal intensity. The observed line shape of the resonance differs significantly from that 75
Chapter 6: Reversible and Irreversible Effects in µc-Si:H Figure 6.11: Absolute values of (a) the spin density, (b) the g-value, and (c) the peak to peak line width as a function of the annealing period. observed in µc-Si:H. In fact, it is impossible to fit the measured data with any combination of the two resonances at g-values of g=2.0043 and g=2.0052. Fitting with three resonance lines might appear promising, but cannot be justified without more experimental evidence. On the other hand, a fit with three signals (either Gaussian or Lorentzian) using as many as 9 free parameters (peak position, width, amplitude for each signal) is most questionable. The absolute values of N S ,g,and∆H pp shown in Fig. 6.11 are therefore extracted from the overall signal without deconvoluting the spectra. The spin density, plotted in panel (a), increases with increasing annealing period. The changes are highest for the highly crystalline porous material (IC RS = 0.82), where the overall N S increases from values of N S (t = 0) = 5×10 16 cm −3 to N S (t = 250h) = 1.5×10 17 cm −3 . With increasing amorphous content the porosity of the material and therefore the active surface area decreases. The increase of N S within 250h is less pronounced, with ∆N S ≈ 2 × 10 16 cm −3 for IC RS = 0.71 material, or even disappears for IRS C = 0.47. The increase in the spin density is accompanied by a shift of the average g-value, which is shown in Fig. 6.11 (b). Again the changes are highest for the porous sample where the g-value increases from g=2.0046 to g=2.0051; the shift becomes less pronounced upon increasing amorphous content. As can be seen in Fig. 6.10, while the oxidation process proceeds, the peak to peak line width of 76
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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
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Chapter 3 Sample Preparation and Ch
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3.1 Characterization Methods Figure
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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 90 and 91: 6.2 Irreversible Oxidation Effects
Page 92 and 93: 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
Page 132 and 133: Bibliography [1] E. Becquerel. Mém
Page 134 and 135: BIBLIOGRAPHY [21] D. Will, C. Lerne
Page 136 and 137: 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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