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

More documents

Recommendations

Info

56 Yun et al. (2006) used AFM to show the process of nucleation and growth at different stages during growth. The images show isolated nuclei forming on the substrate at an epilayer thickness of 0.08 µm during the initial stages of deposition. The nuclei merge at a thickness of 0.13 µm and develop further to form a continuous {100} faced surface at 0.7 µm. They explained that the driving force for the growth to take place through this process is a result of the lattice mismatch between the SiC and Si as well as thermal mismatch. Finally the researchers Sudarshan et al. (2006), Nagasawa et al. (2002), and Jacob et al. (2000) all presented results that are consistent with what is discussed above. 5.3 Crystal Defects in SiC 5.3.1. Introduction The main crystal defects found in epitaxially grown 3C-SiC are stacking faults with their accompanying partial dislocations, twins and inversion domain boundaries. In a TEM study by Jacob et al. (2000) on epitaxially grown 3C-SiC on Si(001) a high density of planar defects lying on {111} planes was found. Defects included stacking faults and microtwins and the authors suggested that the defects were introduced during the growth process to accommodate the large lattice and thermal mismatches between the crystals. Similar findings were reported by Stoemenos et al. (2004) in a TEM study on 300µm thick freestanding 3C-SiC. Microtwins, stacking faults and inversion domain boundaries were observed and their presence attributed to the same reasons as above. Powell et al. (1987) in an extensive microscopy study on 3C-SiC found microtwins, stacking faults and also misfit dislocations accommodating the lattice mismatch. They presented possible mechanisms for the nucleation and growth of the defects and these will be discussed in Sections 5.3.2 and 5.3.3.
57 Furthermore Pirouz et al. (1987), Ho et al. (1999) and Nagasawa et al. (2002) all studying epitaxially grown 3C-SiC on Si (001) found microtwins and stacking faults as the predominant defects in the SiC and attributed their presence to lattice and thermal mismatch. 5.3.2 Accomodation of Misfit and Interfacial Twinning The mechanism for the accommodation of misfit during growth and its relationship to interfacial twinning has been thoroughly explained by Powell et al. (1987). The total misfit, f, between an epilayer and substrate is accommodated by the elastic strain, ε, of planes in the regions of good register and by interfacial dislocations, δ. The spacing of misfit dislocations with Burgers vector b would be S = b/δ. The Si/SiC system has a lattice mismatch of about 20% (f ≈ 0.2). Assuming that the entire misfit is accommodated by misfit dislocations, f = δ and S ≈ 5b. Thus an array of edge misfit dislocations in SiC parallel to the interface with b = a/2 [110] at a spacing of S ≈ 5d110 would accommodate all the misfit. Furthermore it is also frequently observed that where misfit dislocations become irregular, twinning occurs. The twins nucleate at the interface due to coherency stresses resulting from the lattice mismatch. Twinning may be thought of as the motion of partial dislocations with b = a/6 on consecutive {111} planes. Considering the substrate plane to be (001), a pure misfit edge dislocation with Burgers vector a/2 110] [ _ would be the most efficient type of dislocation to accommodate the lattice mismatch having strength 2a / 2 according to Frank’s rule. A shear type dislocation gliding on the (111) plane for example with b = a/2 101] will have an edge component along the 110] direction of half the strength of the pure [ _ edge with 2a / 4 . Thus the shear type dislocation is only half as efficient as the edge misfit dislocation in accommodating the misfit. On the other hand partial dislocations of the type a/6 121] or a/6 211] gliding on a (111) plane will also have an edge [ _ [ _ component with strength 2a / 4 and is just as efficient as the shear type dislocation in misfit accommodation. Furthermore a twin as discussed above may be considered [ _
Page 1 and 2:
Analysis of the Extended Defects in
Page 3 and 4:
My sincere thanks to the following
Page 5 and 6:
OPSOMMING Hierdie dissertasie hande
Page 7 and 8:
4.2.5. Two-Beam Scattering Matrix 4
Page 9 and 10:
Dedicated to my wife and parents
Page 11 and 12:
SUMMARY The dissertation focuses on
Page 13 and 14:
CONTENTS Chapter 1: INTRODUCTION 1
Page 15 and 16:
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 and 68: 5.1 Introduction 53 CHAPTER FIVE LI
Page 69: 55 different orientations. The inte
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
show all

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

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

Delete template?

Save as template?