(a) 100 µm - Helmholtz-Zentrum Berlin

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94 Results to about 30 <strong>µm</strong>. The dependence of the density of newly formed grains on the cooling rate is shown in Fig. 4.35(b). The faster the cooling rate v2 the larger the newly formed nucleation density ρN. The dependence can be approximated by a line through origin with a slope of about 75 min/ ( K mm 2 ). If the cooling velocity v2 is zero, i.e. the sample is not cooled, there is no additional nucleation. Both dependences of the depletion region width L and the nucleation density ρN can be understood considering that the integration time is increased and thus the ef- fective diffusion length is increased. The higher the cooling rate, i.e. the faster the sample is cooled, the shorter the distance the silicon atoms can diffuse. Thus the depletion region is smaller because the atoms do not have enough time to diffuse to the existing growing grains. And due to the same reason the nucleation density is larger. These considerations are used in the discussion chapter to elucidate the mechanism responsible for the layer exchange process. Different interlayers between the initial Al and a-Si layers are investigated. Several Al oxide interlayers as well as an alternative Mo layer are compared. The function of the interlayer is to control the diffusion of silicon into the Al layer. The interlayer separates top and bottom layer throughout the process. Furthermore the interlayer confines the growing silicon grains within the Al layer. It is derived that several interlayers not only oxide layers are suitable. The interlayer has to meet two requirements. It must not be thermally or chemically affected throughout the process but still allow interdiffusion of Al and Si. The preferential orientation of the resulting poly-Si films has been found to depend both on the annealing temperature and the interlayer. Enhancing the preferential (<strong>100</strong>) orientation of the layers is mandatory for optimizing the low temperature epitaxy and thus the resulting solar cells. The use of a heating steps allows to reduce the process time without causing fur- ther nucleation. This result reinforces a model with depletion regions causing the nucleation suppression. A cooling step prior to the heating step leads to a very strong increase of nucleation which is expected to originate from supercooling
4.2 Temperature profiles 95 �� -2 ] ρ N [1 0 3 m m 4 0 3 0 2 0 1 0 0 0 5 0 1 0 0 1 5 0 2 0 0 v [K m in 2 -1 ] 1 5 1 0 5 (a) 0 0 5 0 1 0 0 1 5 0 2 0 0 v [K m in 2 -1 ] (b) Figure 4.35: (a) Depletion region width L and (b) density of newly formed nuclei ρN as a function of the cooling velocity v2.
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Nucleation and growth during the fo
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"Our ignorance is not so vast as ou
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Zusammenfassung Dünne Schichten au
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• Temperatureprofile mit hoher En
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3.2 In-situ optical microscopy . .
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1 Introduction ’Solar power is ho
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por deposition (PECVD) achieved par
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phous silicon interface layer is ex
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2 State of the art This chapter giv
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2.1 Kinetics of phase change 9 Figu
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2.1 Kinetics of phase change 11 [e
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2.2 Solid Phase Crystallization (SP
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2.2 Solid Phase Crystallization (SP
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2.3 Metal-Induced Crystallization (
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2.4 Aluminum-Induced Layer Exchange
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2.5 Current research involving ALIL
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3 Experimental This thesis is focus
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3.1 Sample preparation 39 does not
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3.1 Sample preparation 41 � �
Page 59 and 60: 3.2 In-situ optical microscopy 43 m
Page 61 and 62: 3.2 In-situ optical microscopy 45 B
Page 63 and 64: 3.3 Electron Back Scatter Diffracti
Page 65 and 66: 4 Results In order to understand an
Page 67 and 68: 4.1 Interlayer 51 (a) (b) Figure 4.
Page 69 and 70: 4.1 Interlayer 53 Figure 4.2: TEM c
Page 71 and 72: 4.1 Interlayer 55 c o u n ts [a .u
Page 73 and 74: 4.1 Interlayer 57 R C [% ] 1 0 0 8
Page 75 and 76: 4.1 Interlayer 59 � � ��
Page 77 and 78: 4.1 Interlayer 61 � � ��
Page 79 and 80: 4.1 Interlayer 63 -2 ] N G [m m 8 6
Page 81 and 82: 4.1 Interlayer 65 TA = 450 °C TA =
Page 83 and 84: 4.1 Interlayer 67 (111) (100) (110)
Page 85 and 86: 4.1 Interlayer 69 4.1.2 Molybdenum
Page 87 and 88: 4.1 Interlayer 71 Fig. 4.17 optical
Page 89 and 90: 4.1 Interlayer 73 R C [% ] 1 0 0 8
Page 91 and 92: 4.2 Temperature profiles 75 face la
Page 93 and 94: 4.2 Temperature profiles 77 � �
Page 95 and 96: 4.2 Temperature profiles 79 R C [%
Page 97 and 98: 4.2 Temperature profiles 81 a small
Page 99 and 100: 4.2 Temperature profiles 83 � �
Page 101 and 102: 4.2 Temperature profiles 85 (a) (b)
Page 107 and 108: 4.2 Temperature profiles 91 ��
Page 109: 4.2 Temperature profiles 93 in. Thu
Page 113 and 114: 5 Discussion Two of the most import
Page 115 and 116: 5.1 Definition of three crucial Si
Page 125 and 126: 5.2 The ALILE process in the phase
Page 127 and 128: 5.2 The ALILE process in the phase
Page 129 and 130: 5.3 Depletion regions in the ALILE
Page 131 and 132: 5.4 Comparison of the qualitative m
Page 137 and 138: 5.5 Preferential orientation model
Page 145 and 146: 6 Conclusions In the aluminum-induc
Page 147 and 148: A Preferential orientation calculat
Page 149 and 150: The area of the base of the pyramid
Page 151 and 152: B Abbreviations, symbols and units
Page 153 and 154: symbol unit meaning ∆G a eV activ
Page 155 and 156: Bibliography [1] M. Rogol, S. Doi,
Page 157 and 158: [20] R.W. Bower, R. Baron, J.W. May
Page 159 and 160: [38] J. Jang, J.Y. Oh, S.K. Kim, Y.
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[58] N.-P. Harder, T. Puzzer, P. Wi
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[72] G. Ekanayake, S. Summers, and
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[87] H.R. Philipp and E.A. Taft. An
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list of publications journal papers
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B. Rau, J. Klein, J. Schneider, E.
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(2002), 87. S. Gall, M. Muske, I. S
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tion. Special thank’s go to Dr. M
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10/95-09/98 student electrical engi
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(a) 100 µm - Helmholtz-Zentrum Berlin

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