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Chapter 5 N-Type Doped µc-Si:H In section 4 results of intrinsic films of µc-Si:H with a systematic variation of material structure ranging from highly crystalline to amorphous growth were shown. ESR measurements have been used to determine the spin density N S . However, from these investigations it is not clear how far N S correlates with the defect density in the material and if the spin density N S is a measure of the real defect density N DB . This is the subject of the following section. For this purpose, material prepared with different SC=[SiH 4 ]/([H 2 ]+[SiH 4 ]) and phosphorous doping levels PC =[PH 3 ]/([PH 3 ]+[SiH 4 ]) will be studied. The silane concentration was varied in the range from SC = 2% to 8%, resulting in structure compositions comparable to those studied in Chapter 4. The doping concentrations PC of 1, 5, and 10 ppm were chosen to be of the order of the intrinsic spin density N S (see Fig. 4.5 (a)). To study effects of doping on the position of the Fermi level and the occupation of defect states, electrical dark conductivity σ D and ESR measurements have been performed. 5.1 Structure Characterization In order to obtain a measure of the crystalline volume content, Raman spectra were recorded on both glass and aluminum substrates. The results are summarized in Fig. 5.1 (a), showing the Raman intensity ratio IC RS plotted versus the silane concentration SC. For doping concentrations in the range of 1−10 ppm the transition from highly crystalline to predominantly amorphous growth can be observed. In the highly crystalline growth regime between SC=2% and 5%, the Raman intensity ratio decreases only slightly from IC RS =0.85 to 0.74 and the spectra are dominated by the crystalline signal. Above SC=5% the transition to amorphous growth can be observed. An increasing amorphous phase contribution results in a fairly steep decrease of IC RS between SC=5% and 7%. For silane concentra- 51
Chapter 5: N-Type Doped µc-Si:H Figure 5.1: (a) Raman intensity ratio (IC RS ) for samples deposited on aluminum (closed symbols) and glass (open symbols). (b) Raman spectra of µc-Si:H prepared at SC = 7% with varying doping concentrations of PC =1, 5, and 10 ppm). With increasing doping concentration the crystallinity increases. tions higher than SC=7% the Raman spectra show only the amorphous peak at 480 cm −1 . Comparing samples deposited on glass and aluminum, the well known substrate dependence on the material structure can be observed (compare with Fig. 4.1). Samples deposited on glass in general show a higher amorphous phase contribution and therefore a smaller value of IC RS compared to material deposited on aluminum. This has to be kept in mind as in the following section results from conductivity measurements as well as ESR measurements will be compared, where glass and aluminum substrates were used, respectively. Also with increasing doping concentration PC the Raman intensity ratio increases. This is shown in Fig. 5.1 (b), where for a given silane concentration SC the crystallinity increases with increasing doping concentration. 5.2 Electrical Conductivity Conductivity measurements, as described in section 3.1.3, were performed on films deposited on glass substrates. The results are shown in Fig. 5.2 (a), where the dark conductivities σ D of phosphorous doped material with PC = 1, 5, and 10 ppm are plotted together with conductivity data of undoped material taken from reference [18]. For the undoped material the conductivity σ D decreases only slightly between IC RS =0.82 and 0.47. As a consequence of the structural transition, for material with an IC RS lower than 0.4 σ D decreases by several orders of magnitude, resulting in values below 10 −10 S/cm typical for a-Si:H [65]. Doping effects can 52
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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
Page 14 and 15: Chapter 1 Introduction Solar cells
Page 16 and 17: 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
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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 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
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Chapter 8 Schematic Density of Stat
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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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