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6.1 Metastable Effects in µc-Si:H Figure 6.2: (a) ESR spectra of highly crystalline material (IC RS = 0.82) before and after treatment in HCl, H 2 O, and storage in air atmosphere. Panel (b) shows the measured values of the spin densities, (c) the g-value, and (d) the peak to peak line width ∆H pp before and after treatment, respectively. strates was rinsed in either H 2 OorHCl/H 2 O solution, or was just kept in air atmosphere for 24 hours. In each case ESR spectra were recorded before and after the treatment. The results are shown in Fig. 6.2 (a). The spectra were normalized to the same peak height allowing differences in the line shape to be compared. The vertical dotted lines indicate the resonances with g-values at g=2.0043 and g=2.0052, typically observed in µc-Si:H (see section 2.2.2). Independent of the particular treatment the line shape changes significantly. The intensity of the ESR signal increases for higher g, which is equivalent with the low magnetic field site. The increase of the signal intensity at higher g-values is accompanied by a shift of the zero crossing of the ESR line towards higher values, observable in all spectra. Besides these effects, which are similar for all sample treatments discussed here, slight differences occur for the case of the H 2 O treatment. Here the spectra taken before the treatment already show a higher intensity of the signal at high g- values. However, the characteristic changes upon the treatment and the observed shift of the average g-value are a general trend for all treatments. This indicates that the pre-treatment differences in the ”H 2 O”-spectra are a result of the fact that 65
Chapter 6: Reversible and Irreversible Effects in µc-Si:H instability effects already affected the material before the first measurement has been performed. This is in agreement with the observed values of the spin density N S , the electronic g-value, and the line width ∆H pp plotted in Fig. 6.2 (b, c, d). Independently of the particular treatment one observes an increase of all these three quantities. For all treatments (i) the spin density increases by up to a factor of three, saturating at values of N S ≈ 6 × 10 16 cm −3 , (ii) the electronic g-value shifts to higher values starting from g=2.0044 (2.0045 for H 2 O) and final values of g=2.0046, and (iii) the line width increases from ∆H pp = 6.8 ± 0.1 G (7.3 ± 0.1 G for H 2 O) to 8.7 ± 0.1 G. Quite surprisingly, the final values of N S ,g, and ∆H pp are the same for all treatments. This result clearly indicates that it is not the HCl etching step, which causes the additional increase in N S , the shift of the electronic g-value, and the increased ∆H pp . In fact, the observed changes are essentially the same if the powder is just treated in water and even a simple storage of the material in air leads to a similar effect. The fact that the pre-treatment values of the ”H 2 O”-material are slightly higher, compared to the material treated in HCl and air supports the assumption that in this case instability effects already set in before the first measurement could be performed. The study of different treatments, described above, was performed on material with a pronounced crystallinity. The effects of an increasing amorphous phase is now discussed. For a better understanding of the results shown below, it is important to note, that with increasing amorphous content of the films the film structure may change as well as the film composition. While IC RS = 0.82 material shows a high degree of porosity, IC RS = 0.71 material is still highly crystalline, but compact. Finally IC RS = 0.47 material is prepared at the transition between microcrystalline and amorphous growth and shows a rather compact structure with a high a-Si:H contribution (see section 2.1). Fig. 6.3 (a) shows the ESR spectra of material with three different structure compositions ranging from highly crystalline porous (IC RS = 0.82) over highly crystalline compact material (IC RS = 0.71) to material at the threshold between crystalline and amorphous growth (IC RS = 0.47). The spectra were taken before and after a H 2 O treatment and then normalized in order to show differences in the line shape. Also indicated as vertical dotted lines are the resonances with g-values at g=2.0043 and g=2.0052. Changes in the shape of the ESR spectra can be observed for the IC RS = 0.82 and IRS C = 0.71 material, while on the other hand the line shape of the IC RS = 0.47 spectra remains unchanged upon the H 2O treatment. As for the IC RS = 0.82 material, which was discussed above (see Fig. 6.2), in the IC RS = 0.71 samples the intensity at the high g-value site of the spectra has a larger contribution to the total ESR intensity after the treatment. In Fig. 6.3 (b, c, d) 66
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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
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 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 80 and 81: 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
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
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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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