Measurements

More documents

Recommendations

Info

6.1 Metastable Effects in µc-Si:H sample 1 (see Fig. 6.3). Looking at the initial spectra of this sample, one can not see the typical shoulder at the high g-value site, expected for material exposed to air or water. The reason for the quite constant resonance upon annealing might therefore be a result of a higher stability of the material upon treatment in air or water. The transition material (I RS = 0.47) shows the same behavior like the IC RS C = 0.82 material. The ESR signal intensity decreases after annealing in argon atmosphere at T = 80 ◦ C. As expected from the instability results described in section 6.1.1 the effect is less pronounced, compared to the highly crystalline porous material. As already mentioned above, the decreasing ESR signal intensity directly scales with N S . In fact, from Fig. 6.6 it is clear that the spin density decreases for the IC RS = 0.82 and 0.47 material, as a function of annealing period t ann. While the increase of the spin density exposure to air or water has been attributed to an increase of the number of spins with a g-value of g=2.0052, the annealing also just affects the db 2 resonance. This is shown in Fig. 6.7 (a, b), where the spin densities of the individual resonances db 1 and db 2 are plotted versus t ann . Except for the IC RS = 0.71 material, N db 2 decreases, while N db1 remains constant. The decrease of the spin density at g=2.0052 is accompanied by a shift of the average g-value and a decrease of the line width ∆H pp . Both quantities are plotted in Fig. 6.7 (c) and (d), respectively. For the IC RS = 0.82 material, annealing for 250 hours the spin density decreases from 4 × 10 16 cm −3 to 9 × 10 15 cm −3 , while the average g-value shifts from 2.0047 to 2.0044 and line width decreases from ∆H pp = 8.8 G to 7.6 G. The final values after 250 hours annealing in argon atmosphere at 80 ◦ C are close to the initial values of the material before the exposure to air, as can be seen from Fig. 6.3 and 6.5. In fact, the increase of the spin density N db2 , the shift of the g-value, and the increase of the line width ∆H pp can be reversed by a simple annealing step in argon atmosphere at temperatures of T = 80 ◦ C. Interestingly, the reversible behavior in the ESR signal, particular the strong changes found in IC RS = 0.82 material upon air-exposure and annealing can be repeated many times without any sign of fatigue. However, while the spin density decreases upon annealing the question arises at what point the decrease will saturate. After 250 hours N S shows an asymptotic behavior, but still does not saturate. Assuming the involved processes are thermally activated an increase of the temperature might accelerate the procedure. Annealing/air-exposure cycles have therefore been performed at a temperature of T = 160 ◦ C. The temperature was carefully chosen to considerably activate the process without leading to a desorption of hydrogen, which in term would lead to the creation of additional dangling bond defects. Fig. 6.8 shows the results 1 Note, that the samples used for annealing are not the same as the once used for the treatments in H 2 O. However, the particular deposition parameters have been kept constant. 71
Chapter 6: Reversible and Irreversible Effects in µc-Si:H Figure 6.7: The absolute values of N S for the individual lines at (a) g=2.0052 and (b) g=2.0043 were determined by deconvoluting the spectra shown in Fig. 6.6. In panel (c) and (d) the extracted values of g and ∆H pp are plotted versus the annealing period. obtained from annealing the highly crystalline porous material (IC RS = 0.82) in argon atmosphere. For the experiment the sample was stored in air for about 50 hours (upper trace in Fig. 6.8). After annealing the material at T = 160 ◦ C for one hour, the ESR spectrum as shown as the middle trace in Fig. 6.8 was recorded. Quite surprisingly, the spectrum shows a strong contribution of the conduction electron resonance, after annealing (compare section 2.2.2). This suggests a considerable shift of the Fermi level up into the conduction band-tail. To determine N S of the individual lines, the spectra were deconvoluted as indicated by the gray lines, shown in Fig. 6.8. The spin densities of the two resonances at g=2.0043 and g=2.0052 decrease as a result of the annealing. The particular values are plotted in table 6.1. The high number of electrons trapped in conduction band-tail states (N CE = 6×10 16 cm −3 ) suggests a considerable background doping in this sample. Quite surprisingly, these changes are reversible and the material can be treated back to its initial state by simply exposing it to air atmosphere, as shown in the lower trace of Fig. 6.8. 72
Page 1 and 2:
Forschungszentrum Jülich in der He
Page 4 and 5:
Forschungszentrum Jülich GmbH Inst
Page 6 and 7:
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
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 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
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.
Page 138 and 139:
BIBLIOGRAPHY [66] P.W. Anderson. Ab
Page 140 and 141:
BIBLIOGRAPHY [93] J.W. Orton and M.
Page 142 and 143:
BIBLIOGRAPHY [121] J.R. Haynes and
Page 144 and 145:
BIBLIOGRAPHY [148] W. Luft and Y.S.
Page 146 and 147:
BIBLIOGRAPHY [170] G.N. Advani, R.
Page 148 and 149:
List of Publications 1. T. Dylla, R
Page 150 and 151:
Acknowledgments At this point, I wa
Page 152 and 153:
Schriften des Forschungszentrums J
Page 154 and 155:
Page 156 and 157:
Page 159:
Forschungszentrum Jülich in der He
show all

Measurements

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?