Measurements

More documents

Recommendations

Info

Chapter 3 Sample Preparation and Characterization This chapter summarizes the experimental methods used to prepare and characterize the material investigated in this work. In the first section the measurement techniques applied to study the material properties are discussed. The second part describes the basics of the deposition techniques, namely plasma enhanced chemical vapor deposition (PECVD) and hot wire chemical vapor deposition (HWCVD). As for different characterization methods different substrates and device structures are needed, the last section will provide an overview of the particular sample preparations and treatments. 3.1 Characterization Methods The aim of this section is describe the potential, but also the limitations of the individual techniques used for the material characterization. In this study, Raman spectroscopy was used to determine the crystallinity of the material, paramagnetic states were studied by electron spin resonance (ESR) and transport properties were investigated using conductivity measurements and transient photocurrent experiments (TOF). 3.1.1 Raman Spectroscopy Raman spectroscopy can provide detailed information about the vibrational properties of solids, liquids, and gases. A detailed description of the underlying physics can be found in the literature [105, 106]. Reviews of the application to µc-Si:H can be found in [107, 108] and a detailed description of the setup used in this work 19
Chapter 3: Sample Preparation and Characterization in [109, 52]. Here Raman spectroscopy has been used to determine the crystalline volume content of the µc-Si:H material. As described in section 2.1 µc-Si:H is a phase mixture of crystalline and amorphous material. A typical Raman spectrum, as shown in Fig. 3.1, is a convolution of a crystalline and an amorphous spectrum. Spectra of crystalline silicon are dominated by a peak at 520 cm −1 attributed to the transversal optical (TO) phonon. Due to the finite grain size and internal stress in µc-Si:H this peak shifts to lower values (usually found at 518 cm −1 ) and the peak width increases [110, 107]. As a result of the absence of long range translation symmetry in a-Si:H, the quantum number ⃗k is no longer well-defined and the excitation of a phonon is possible without restriction of ⃗k preservation. In a-Si:H, one therefore observes a broad intensity distribution of the TO-phonon at 480 cm −1 . Besides these two peaks a third peak at around 492 cm −1 is often observed in µc-Si:H Raman spectra. This peak is a result of stacking faults in the crystalline phase, also referred to as wurtzite peak [111]. To account for the asymmetry, the crystalline peak was fitted by two Gaussian lines centered at 518 cm −1 and 505 cm −1 . As a measure of the crystallinity, the Raman intensity ratio IC RS was used, defined as I RS C = I 518 + I 505 I 518 + I 505 + I 480 . (3.1) For a given sample, IC RS was determined by de-convoluting the spectra into three contributions at wave numbers of 518, 505 and 480 cm −1 . Although IC RS is related to the volume content of crystalline and disordered phase this evaluation must be used carefully. The Raman cross sections for crystalline and amorphous silicon are different and additionally they depend on the wavelength of the incident laser light. Measured by Tsu et al. [112], the cross section ratio at λ = 496.5 nm is σ c /σ a =0.88. Additionally, grain boundaries may lead to a signal at 480 cm −1 [113]. For these reasons IC RS can be considered as a lower limit of the crystalline volume content. Information about the distribution of the crystalline volume fraction in the growth direction can be obtained by using different excitation wavelengths λ. In this work laser wavelengths of 488 nm and 647 nm were used, that corresponds to an information depth 1 of 150 nm and 800 nm, respectively. The validity of the determination of the crystallinity by Raman spectroscopy used in this work is still under discussion. While Ossadnik et al. [114] found no correlation between the Raman intensity ratio and the crystalline volume fraction obtained from X-ray diffraction measurements, recent work in the Juelich group 1 The information depth is defined as half of the absorption depth (depth where the signal is attenuated to a fraction of 1/e). 20
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 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 80 and 81: 6.1 Metastable Effects in µc-Si:H
Page 82 and 83:
6.1 Metastable Effects in µc-Si:H
Page 84 and 85:
Page 86 and 87:
Page 88 and 89:
6.2 Irreversible Oxidation Effects
Page 90 and 91:
Page 92 and 93:
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 102 and 103:
Page 104 and 105:
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?