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4.3 ESR Signals and Paramagnetic States in Intrinsic µc-Si:H Figure 4.6: g-values as a function of IC RS of material prepared (a) VHF-PECVD and (b) HWCVD deposited at various substrate temperatures. The values for the VHF-PECVD material were taken from reference [17]. For the HWCVD material, again the highest N S is always found for material with the highest crystallinity. Within the crystalline regime, the spin density decreases considerably with increasing amorphous content for all substrate temperatures T S . For material dominated by amorphous phase content (IC RS < 0.4), the spin density increases, rather than staying constant or decreasing as observed for the PECVD material. Only for the highest T S of 450 ◦ C the spin density decreases monotonously, however at very high values of N S > 10 17 cm −3 . Finally, independent of the particular structure composition, N S increases significantly when the substrate temperature is increased by up to three orders of magnitude for IC RS ≈ 0.5. It is important to note that the lowest spin densities of N S = 4 × 10 15 cm −3 are observed for material prepared at T S = 185 ◦ C and a crystalline volume fraction of IC RS ≈ 0.4, and that solar cells prepared under similar conditions have shown maximum efficiencies of η = 9.4% [162]. The corresponding average g-values are plotted versus I RS in Fig. 4.6. For the PECVD material shown in Fig. 4.6 (a), the average g-value shifts from a value of 2.0043 to 2.0051, when going from crystalline to amorphous structure. This means that with increasing amorphous content the g-value is clearly shifted to higher values, however without reaching the value of 2.0055 usually found in a- Si:H. As shown in Fig. 4.6 (b), the g-values for material prepared with HWCVD are generally higher (note the different scaling of the y-axis in panels (a) and (b)). The variations as a function of structure are considerably less for the HW-material. Again, even for material with no contribution of the crystalline phase in the Raman signal, the g-values do not reach the typical value of 2.0055 found in a-Si:H. Generally, one observes an increasing g-value for increasing substrate temperature over the entire range of I RS C . 45 C
Chapter 4: Intrinsic Microcrystalline Silicon Figure 4.7: g-value vs. spin density N S of material prepared with HWCVD for three structure compositions ranging from highly crystalline to transition material. The data are taken from Fig. 4.5 (b) and 4.6 (b). Comparing Fig. 4.5 (b) and Fig. 4.6 (b), one can observe that both N S and the g-value increase with increasing substrate temperature T S . In Fig. 4.7 the g- value is plotted versus N S for three different structure compositions, ranging from highly crystalline to material prepared close to the transition between microcrystalline and amorphous growth. The values of N S and g were taken from Fig. 4.5 and 4.6, respectively; the data points in Fig. 4.8 therefore correspond to material prepared at different substrate temperatures. Although there is some scatter of the data for the IC RS ≈ 0.65 material, there is a clear correlation between this two quantities: For increasing spin density the g-value is clearly shifted to higher values. This can be observed for all structure compositions between IC RS = 0.74 and 0.55. Assuming that within the crystalline regime the ESR signal is a composition of only two resonances at g=2.0043 and g=2.0052, the shift of the average g-value is a result of a change in the ratio of these contributions. This of course also assumes that the g-value of each line does not shift for different deposition conditions, which is a rather strong postulation. Keeping this in mind, the results indicate that the increasing spin density N S , as a function of increasing T S , is caused by an increasing number of paramagnetic states that belong to the db 2 resonance. The fact that high quality µc-Si:H material with no discernable crystalline signal in the Raman signal does not show the typical a-Si:H g-value of 2.0055 was a little puzzling. Material has therefore been prepared with even higher silane concentrations ranging from SC = 9% to 100% using VHF-PECVD. Spin densities and g-values measured for this material are plotted in Fig. 4.8 along with the 46
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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
Page 8 and 9: Abstract The electronic properties
Page 10 and 11: Contents 1 Introduction 1 2 Fundame
Page 12 and 13: 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 28 and 29: 2.3 Charge Carrier Transport influe
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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
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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
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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
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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.
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Page 74 and 75: 5.7 Summary Figure 5.7: Schematic b
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7.4 Multiple Trapping in Exponentia
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7.5 Discussion Table 7.2: Multiple
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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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