Analysis of the extended defects in 3C-SiC.pdf - Nelson Mandela ...

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54 The critical radius and energy barrier for the formation of stable nuclei both depend on γf/s. The film/substrate interfacial energy in turn depends on the bonding across the interface where the existence of elastic strains and dangling bonds increases its value and thus increases r and ΔG. Consequently epitaxially oriented nuclei will have a lower interfacial energy and a smaller critical radius and energy of formation barrier. Misoriented nuclei will have a larger interfacial energy with a larger critical radius and energy of formation barrier than oriented nuclei and will be subcritical and dissolve away. The rate of nucleation, N, is proportional to exp(-ΔG/kT) and thus many more oriented than misoriented nuclei will form. However the film/substrate interfacial energy is expected to be a function of temperature and its contribution to the energy of formation barrier decreases with increasing temperature. This in turn reduces the anisotropy between oriented and misoriented nuclei formation and it is expected that at higher temperatures their deposition rates become more equal. This is evidenced by the fact that the growth of SiC at higher temperatures results in a polycrystalline structure. If the film/substrate energy is considered the energy of oriented nuclei will be in a global minima of the energy function with an orientation relationship between the substrate and nucleus of (001)Si||(001)SiC ; 110] Si|| 110] SiC. However Pirouz et al. (1987) mentioned that local [ _ [ _ minima in the energy function also exists for other orientations. For example a nuclei twinned on a 111) plane relative to an epitaxial one will have the orientation ( _ relationship with respect to the substrate as (001)Si|| 221) SiC ; 110] Si|| 114] ( _ [ _ [ _ SiC . These types of nuclei are expected to have a lower film/substrate interfacial energy than misoriented nuclei but higher than oriented. Thus a fraction of the stable nuclei will have a twinned orientation relationship. Further, the lateral growth of the twinned nuclei will be slower than that of the oriented ones and will grow easier in directions inclined to the interface. As a result they tend to growth thin and long within the film. Growth at 1380°C results in migration of the twinning boundaries and the consumption or decrease in the volume of the twins. Powell et al. (1987) in a different publication explains that during the initial stages of deposition a large number of supracritical nuclei form on the Si substrate with
55 different orientations. The interfacial energy of the epitaxially oriented nuclei is lower than that of the misoriented ones and as a result the former nuclei will have a relatively faster lateral growth whereas the latter grows preferentially in vertical directions. Once the different nuclei meet a grain boundary stress results between the nuclei which tends to cause the epitaxial nuclei to grow at the expense of the misoriented. This is proportional to the difference in interfacial energies between the two nuclei, the surface areas of the grains and the grain boundary energy. If the substrate is heated to the growth temperature and the silane and propane are introduced, the nuclei will grow vertically and laterally in a three dimensional manner called one-step deposition. This causes the vertical growth of the grains to occur faster than lateral growth of the epitaxially oriented ones causing a polycrystalline aggregate. In the two-step process, the island nuclei start forming during the ramping process at much lower temperatures with their growth being predominantly two-dimensional with Si coming from the substrate. In the extreme case where only propane is admitted in the ramping stage with no Si present in the vapour phase vertical growth is inhibited. Due to the predominant lateral growth, epitaxially oriented nuclei grow much faster than misoriented ones which rapidly consume misoriented grains before bulk deposition takes place. Fig. 5.1. Atomic force microscopy images of 3C-SiC epilayers having different thicknesses: (a) 0.08; (b) 0.13; (c) 0.7 and (d) 3.7 µm (from Yun et al. (2006)).
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Analysis of the Extended Defects in
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My sincere thanks to the following
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OPSOMMING Hierdie dissertasie hande
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4.2.5. Two-Beam Scattering Matrix 4
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Dedicated to my wife and parents
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SUMMARY The dissertation focuses on
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CONTENTS Chapter 1: INTRODUCTION 1
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1 CHAPTER ONE INTRODUCTION Silicon
Page 17 and 18: 2.1. Introduction 3 CHAPTER TWO OVE
Page 19 and 20: 2.2.2 The Zinc-Blende Structure 5 T
Page 21 and 22: 2.3 Point Defects, Defect Migration
Page 23 and 24: v m Em vm0 exp( ) (2.2) kT 9 wher
Page 25 and 26: 11 explained and the concept of par
Page 27 and 28: 13 Straight dislocations furthermor
Page 29 and 30: 2.5 Partial Dislocations and Slip 1
Page 31 and 32: 17 Fig. 2.13. The geometrical setup
Page 33 and 34: 19 extrinsic stacking faults are th
Page 35 and 36: 2.8 Twinning 21 Twinning is a proce
Page 37 and 38: 23 Fig. 2.20. The process of vacanc
Page 39 and 40: S n Td (3.2) 25 and is also referr
Page 41 and 42: 27 where a = a0(Z1 2/3 + Z2 2/3 ) -
Page 43 and 44: 29 Using this expression, curves of
Page 45 and 46: 31 As stated previously hard-sphere
Page 47 and 48: 33 where A is the atomic weight. Th
Page 49 and 50: 35 a vacancy dislocation loop if th
Page 51 and 52: 37 Fig. 4.1. (a) A wave incident on
Page 53 and 54: 39 Consider Fig. 4.2 which illustra
Page 55 and 56: 41 V0 is the mean inner potential o
Page 57 and 58: 43 beam left-hand side g' = 0 g' =
Page 59 and 60: 45 In addition another set of indep
Page 61 and 62: 47 When this is incorporated into t
Page 63 and 64: S ( s , z ) e T i Se ( / 0 )
Page 65 and 66: z0 z2 . xn cos and (4.47) D 1 proj
Page 67: 5.1 Introduction 53 CHAPTER FIVE LI
Page 71 and 72: 57 Furthermore Pirouz et al. (1987)
Page 73 and 74: 59 intersection of the fault, the f
Page 75 and 76: 61 each nuclei because of the low s
Page 77 and 78: 63 (2000) found that subsequent ann
Page 79 and 80: 6.3.1 Ion Range and Defect Producti
Page 81 and 82: 67 Fig. 6.3. Total number of displa
Page 83 and 84: 7.1 Introduction 69 CHAPTER SEVEN R
Page 85 and 86: Fig. 7.2. Simulated diffraction pat
Page 87 and 88: 73 Fig. 7.3. A HRTEM image of the S
Page 89 and 90: 75 Fig. 7.5. The stacking fault sel
Page 91 and 92: (Si/ni) 2 0.000018 0.000016 0.00001
Page 93 and 94: 79 may be concluded that the initia
Page 95 and 96: 81 Fig. 7.11. Bright field TEM micr
Page 97 and 98: 83 Fig. 7.12 which was obtained by
Page 99 and 100: 85 Fig. 7.13. Bright-field TEM micr
Page 101 and 102: 87 (a) (b) Fig. 7.15. The (a) exper
Page 103 and 104: 89 In the following paragraphs the
Page 105 and 106: Fig. 7.18. CBED pattern taken of th
Page 107 and 108: 93 Table 7.5. The measured paramete
Page 109 and 110: 7.4.2 Results 95 Fig. 7.22. Bright-
Page 111 and 112: 97 Twin platelets on {111} planes
Page 113 and 114: 99 REFERENCES Blumenau, A.T., Jones
Page 115 and 116: 101 Hull, D., Bacon, D.J. : (1984)
Page 117: 103 Smith, D.J., Jepps, N.W. and Pa
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