Vapor Crystal Growth and Characterization (eBook)

Preface 6
Acknowledgements 8
Contents 9
Abbreviations 13
1 Introduction 15
1.1 Group II–VI Wide Bandgap Compound Semiconductors 15
1.2 Crystallization by Physical Vapor Transport 17
References 20
2 Fundamentals of Physical Vapor Transport Process 23
2.1 Sublimation of Source Materials 24
2.1.1 Vapor Pressures of Pure Elements 24
2.1.2 Thermodynamics of Solid and Vapor Phases in Compound Semiconductors 25
2.1.3 Partial Pressure Measurements 29
2.1.4 Thermodynamic Analyses 38
2.2 Physical Vapor Transport Process (One-Dimensional Diffusion Model) 40
2.2.1 Diffusive Transport in Binary Systems 40
2.2.2 Diffusive Transport in Multi-nary Systems 44
2.2.3 Diffusive Transport with Residual Gas of Impurities 45
2.2.4 Summary of One Dimensional Diffusion Analysis 47
2.2.5 Convective Transport 47
Appendix 49
A.1 Thermophysical Properties of Vapor Phase 49
A.2 Thermophysical Properties of a Typical ZnSe PVT Growth System 51
References 51
3 Vapor Transport Rate (Mass Flux) Measurements and Heat Treatments 53
3.1 Mass Flux of CdS by PVT 54
3.1.1 CdS Ampoules Sealed Under Vacuum 54
3.1.2 CdS Ampoules Sealed with Ar Pressure 58
3.1.3 CdS Samples Annealed Under Controlled Cd Over-Pressure 60
3.1.4 Summary on PVT of CdS 61
3.2 Mass Flux and Heat Treatments of CdTe 62
3.2.1 Vapor Phase Stoichiometry 62
3.2.2 Heat Treatments of CdTe for PVT 63
3.3 Mass Flux and Heat Treatments for ZnSe System 67
3.3.1 In-Situ Dynamic Mass Flux Measurements 67
3.3.2 Heat Treatments of Source Materials 68
3.3.3 Measurements of Residual Gas Pressure and Composition 70
3.3.4 Simultaneous Measurements of Partial Pressure and Mass Flux in PVT of ZnSe 72
3.3.5 Optimum Heat Treatment Procedures for ZnSe Starting Materials 74
3.3.6 Summary of Heat Treatment of Starting Material of ZnSe 77
3.4 Mass Fluxes in ZnSe-Related Ternary Systems 78
3.4.1 One-Dimensional Diffusion Model for Ternary Case 78
3.4.2 Mass Flux of PVT for ZnSe1?xTex System 79
3.4.3 Mass Flux of PVT for ZnSe1?xSx System 81
3.4.4 Mass Flux of Zn1?xCdxSe System from One-Dimensional Diffusion Model 85
3.4.5 Summary of Mass Flux of ZnSe-Related Ternary Systems 85
References 86
4 Crystal Growth 88
4.1 Growth Ampoule Preparations 88
4.2 Heat Treatments of Starting Materials 90
4.3 Crystal Growth Environments 92
4.3.1 Temperature Profile 92
4.3.2 Growth Configurations 93
4.3.3 Crystal Growth of ZnSe by PVT 95
4.3.4 Crystal Growth of ZnSe Doped with Transition Metals by PVT 97
4.3.5 Crystal Growth of ZnSeTe by PVT 98
4.3.6 Crystal Growth of CdTe by PVT 101
4.3.7 Crystal Growth of CdS by PVT 103
4.3.8 Crystal Growth of ZnTe by PVT 104
4.4 In-situ Real Time Optical Monitoring During Growth 104
4.4.1 Optical Absorption Measurements 105
4.4.2 Optical Interferometry Measurements 107
4.5 Recent Advancement on the Enhancement of Transport Rate by PVT 114
References 119
5 Residual Gas Measurements and Morphology Characterization on Grown Crystals 121
5.1 Residual Gas Measurements 122
5.2 Morphology of the Grown Crystals 124
5.2.1 Self-seeded Grown Crystals of ZnSe in Horizontal Configuration 124
5.2.2 Self-seeded Grown Crystals of ZnSe in Vertical Configuration 127
5.2.3 Seeded Grown Crystals of ZnSe 130
5.2.4 Analysis on Contactless Growth 130
5.2.5 Growth Kinetics 136
5.2.6 Growth Direction from X-ray Diffraction 138
5.2.7 Transition Metal Doped Crystals of ZnSe 139
5.2.8 Morphology of Grown Crystals of ZnSeTe 140
5.2.9 Morphology of Grown Crystals of CdTe 141
5.2.10 Morphology of Grown Crystals of CdS 144
5.2.11 Morphology of Grown Crystals of ZnTe 147
References 147
6 Characterizations on Crystalline Structures and Defect Distributions 149
6.1 Synchrotron White Beam X-ray Topography and High Resolution X-ray Diffraction Analysis 150
6.1.1 ZnTe Crystals Grown by Self-seeded Horizontal PVT 150
6.1.2 ZnSe Crystals Grown by Self-seeded Horizontal PVT 158
6.1.3 High Resolution Triple X-ray Diffraction (HRTXD) 160
6.1.4 ZnSe Crystals Grown by Self-seeded Vertical PVT 165
6.1.5 ZnSe Crystals Grown by Seeded PVT 165
6.2 Chemical Etching 169
6.2.1 Etching of ZnSe Crystals 170
6.2.2 Etching of CdTe Crystals 170
6.2.3 Etching of CdS Crystals 171
6.3 Cathodoluminescence (CL) 172
6.4 Characterization on Distributions of Impurities and Point Defects 173
6.4.1 Secondary Ion Mass Spectroscopy (SIMS) 173
6.4.2 Photoluminescence (PL) Spectroscopy 177
6.5 Impurity and Dopant Analyses on ZnSe Crystals by Glow Discharge Mass Spectroscopy (GDMS) 189
6.6 Dopant Levels in Cr-Doped ZnSe Crystals Measured by Optical Absorption 190
6.7 Characterizations of ZnSeTe Crystals 191
6.7.1 Compositional Variation by Wavelength Dispersive X-ray Spectroscopy (WDS) 191
6.7.2 Compositional Variation by Optical Transmission Measurements 196
6.7.3 Axial Compositional Variation by Precision Density Measurements 198
References 199
7 Measurements on Thermal and Electrical Properties and Characterizations on Annealed Samples 201
7.1 Thermal, Electrical Conductivity and Seebeck Coefficient of CdTe Grown by PVT 201
7.1.1 Thermal Conductivity 202
7.1.2 Electrical Conductivity 203
7.1.3 Seebeck Coefficient 205
7.2 Effects on Post-growth Annealing of CdS Crystals Grown by PVT 206
References 209
8 Two-Dimensional and Three-Dimensional Numerical Simulation of Vapor Transport Process 210
8.1 The Problem Set Up 211
8.2 Governing Equations 211
8.3 Benchmark Simulations 213
8.4 The Zn–Se System with a Residual Gas Component 215
8.4.1 Two-Dimensional Calculation 217
8.4.2 Three-Dimensional Calculations 221
8.4.3 Limitations of Mathematical Modeling and Future Developments 224
References 226