Zinc Oxide Materials for Electronic and Optoelectronic Device Applications

The three coeditors, Dr. Cole W. Litton, Dr. Donald C. Reynolds and Dr. Thomas C. Collins, are internationally recognized experts in field of the physics of semiconductors, with an emphasis on the optical, electrical and structural properties and crystal growth of these materials, especially zinc oxide and the other Group II-VI semiconductor materials, as well as the III-V compound semiconductor materials and their electronic and optoelectronic devices. Each of the editors has authored more than 500 scientific/technical papers, book chapters, and technical/scientific books over professional careers that have spanned much of the past 30 to 40 years.

Preface xvii

List of Contributors xxi

1 Fundamental Properties of ZnO 1
T. C. Collins and R. J. Hauenstein

1.1 Introduction 1

1.1.1 Overview 1

1.1.2 Organization of Chapter 2

1.2 Band Structure 2

1.2.1 Valence and Conduction Bands 2

1.3 Optical Properties 5

1.3.1 Free and Bound Excitons 5

1.3.2 Effects of External Magnetic Field on ZnO Excitons 6

1.3.3 Strain Field 8

1.3.4 Spatial Resonance Dispersion 9

1.4 Electrical Properties 10

1.4.1 Intrinsic Electronic Transport Properties 10

1.4.2 n-type Doping and Donor Levels 11

1.4.3 p-type Doping and Dopability 13

1.4.4 Schottky Barriers and Ohmic Contacts 17

1.5 Band Gap Engineering 19

1.5.1 Homovalent Heterostructures 20

1.5.2 Heterovalent Heterostructures 22

1.6 Spintronics 22

1.7 Summary 25

References 25

2 Optical Properties of ZnO 29
D. C. Reynolds, C. W. Litton and T. C. Collins

2.1 Introduction 29

2.2 Free Excitons 29

2.3 Strain Splitting of the G5 and G6 Free Excitons in ZnO 35

2.4 Photoluminescence from the Two Polar Faces of ZnO 36

2.5 Bound-Exciton Complexes in ZnO 38

2.6 Similarities in the Photoluminescence Mechanisms of ZnO and GaN 46

2.7 The Combined Effects of Screening and Band Gap Renormalization on the Energy of Optical Transitions in ZnO and GaN 51

2.8 Closely Spaced Donor–Acceptor Pairs in ZnO 55

2.9 Summary 58

References 58

3 Electrical Transport Properties in Zinc Oxide 61
B. Claflin and D. C. Look

3.1 Introduction 61

3.2 Hall-Effect Analysis 62

3.2.1 Single-Band Conduction 62

3.2.2 Two-Band Mixed Conduction 65

3.2.3 Conducting Surface Layers 66

3.3 Donor States and n-type Doping 66

3.3.1 Native Point Defects – Donors 68

3.3.2 Substitutional Donors 69

3.4 Hydrogen 69

3.5 Acceptor States and p-type Doping 70

3.5.1 Native Point Defects – Acceptors 71

3.5.2 Substitutional Acceptors 72

3.6 Photoconductivity 76

3.7 Summary 78

References 78

4 ZnO Surface Properties and Schottky Contacts 87
Leonard J. Brillson

4.1 Historical Background of Schottky Contacts on ZnO 87

4.1.1 ZnO Surface Effects 88

4.1.2 Early Schottky Barrier Studies 90

4.2 Recent Schottky Barrier Studies 91

4.2.1 Surface Cleaning in Vacuum 91

4.2.2 Surface Cleaning Effects on Impurities and Defects 92

4.3 The Influence of Surface Preparation on Schottky Barriers 93

4.4 The Influence of Defects on Schottky Barriers 97

4.5 The Influence of ZnO Polarity on Schottky Barriers 102

4.6 The Influence of Chemistry 103

4.7 Charge Transport and Extended Metal–ZnO Schottky Barriers 108

4.8 Conclusion 110

Acknowledgements 110

References 110

5 Native Point Defects and Doping in ZnO 113
Anderson Janotti and Chris G. Van de Walle

5.1 Introduction 113

5.2 Theoretical Framework 114

5.3 Native Point Defects 115

5.3.1 Oxygen Vacancies 117

5.3.2 Zinc Interstitials 119

5.3.3 Zinc Antisites 120

5.3.4 Zinc Vacancies 121

5.3.5 Defect Migration 121

5.4 Donor Impurities 125

5.4.1 Aluminum, Gallium and Indium 125

5.4.2 Fluorine 125

5.4.3 Hydrogen 125

5.5 Acceptor Impurities 129

5.5.1 Lithium 129

5.5.2 Copper 129

5.5.3 Nitrogen 129

5.5.4 Phosphorous, Arsenic and Antimony 130

5.5.5 Co-Doping 130

5.6 Isoelectronic Impurities 131

Acknowledgements 131

References 131

6 Spectral Identification of Impurities and Native Defects in ZnO 135
B.K. Meyer, D.M. Hofmann, J. Stehr and A. Hoffmann

6.1 Introduction 135

6.2 Optical Spectroscopy 136

6.2.1 Excitons Bound to Shallow Donors 136

6.2.2 Recombinations Caused by Nitrogen and Arsenic Doping 145

6.3 Magnetic Resonance Investigations 153

6.3.1 Shallow Donors 154

6.3.2 Deep Level Defects 158

6.3.3 Extrinsic Acceptors: Li, Na and N 161

6.3.4 Intrinsic Acceptors 166

References 166

7 Vapor Transport Growth of ZnO Substrates and Homoepitaxy of ZnO Device Layers 171
Gene Cantwell, Jizhi Zhang and J.J. Song

7.1 Introduction 171

7.2 Transport Theory and Comparison with Growth Data 172

7.3 Characterization 175

7.3.1 Crystallinity 175

7.3.2 Purity 176

7.3.3 Electrical 177

7.3.4 Optical 178

7.4 In-situ Doping 180

7.5 ZnO Homoepitaxy 181

7.5.1 Substrate Preparation 182

7.5.2 Homoepitaxial Films on c-plane SCVT ZnO Substrates 183

7.5.3 ZnO Homoepitaxial Films on a-plane SCVT ZnO Substrates 185

7.6 Summary 185

Acknowledgement 186

References 186

8 Growth Mechanisms and Properties of Hydrothermal ZnO 189
M. J. Callahan, Dirk Ehrentraut, M. N. Alexander and Buguo Wang

8.1 Introduction 189

8.2 Overview of Hydrothermal Solution Growth 190

8.3 Thermodynamics of Hydrothermal Growth of ZnO 190

8.3.1 Solubility of ZnO in Various Aqueous Media 190

8.3.2 ZnO Phase Stability in H2O System 191

8.4 Hydrothermal Growth Techniques 194

8.4.1 Hydrothermal Growth of ZnO Powder 194

8.4.2 Hydrothermal Crystal Growth of ZnO Single Crystals 194

8.4.3 Industrial Growth of Large ZnO Crystals 197

8.5 Growth Kinetics of Hydrothermal ZnO 200

8.5.1 Crystallographic Structure of Hydrothermal ZnO 200

8.5.2 Growth Rates of the Crystallographic Facets of Hydrothermal ZnO 200

8.6 Properties of Bulk Hydrothermal ZnO 205

8.6.1 Extended Imperfections (Dislocations, Voids, etc.) and Surface Studies 205

8.6.2 Impurities 208

8.6.3 Electrical Properties 210

8.6.4 Optical Properties 213

8.6.5 Etching and Polishing 215

8.7 Conclusion 217

Acknowledgements 217

References 218

9 Growth and Characterization of GaN/ZnO Heteroepitaxy and ZnO-Based Hybrid Devices 221
Ryoko Shimada and Hadis Morkoç

9.1 Introduction 221

9.2 Growth of GaN/ZnO 222

9.3 Compositional Analysis 230

9.4 Structural Analysis 232

9.5 Surface Studies 235

9.6 Optical Properties 237

9.6.1 Transmission Analysis 237

9.6.2 Cathodoluminescence Analysis 239

9.6.3 Photoluminescence Analysis 242

9.7 Electrical Properties 249

9.8 GaN/ZnO Hybrid Devices 252

9.8.1 Hybrid ZnO/GaN Heterojunction LED 253

9.8.2 ZnO-based Hybrid Microcavity 259

9.9 Conclusions 261

Acknowledgements 262

References 262

10 Room Temperature Stimulated Emission and ZnO-Based Lasers 265
D.M. Bagnall

10.1 Introduction 265

10.2 Emission Mechanisms 266

10.3 Stimulated Emission 267

10.3.1 Bulk ZnO 267

10.3.2 Epitaxial Layers 267

10.3.3 Quantum wells and Superlattices 270

10.3.4 ZnMgO/ZnO Structures 270

10.3.5 ZnO/ZnCdO Structures 272

10.4 Zinc Oxide Lasers 274

10.4.1 Introduction 274

10.4.2 Microstructural Lasers 275

10.4.3 Powder Lasers 278

10.4.4 Nanowire Lasers 279

10.4.5 ZnO Laser Diodes 280

10.5 Conclusions 281

References 282

11 ZnO-Based Ultraviolet Detectors 285
Jian Zhong and Yicheng Lu

11.1 Introduction 285

11.2 Photoconductivity in ZnO 288

11.2.1 Persistent Photoconductivity 293

11.2.2 Negative Photoconductivity 295

11.3 ZnO Film-Based UV Photodetectors 297

11.3.1 Photoconductive UV Detector 297

11.3.2 Schottky Barrier UV Photodetectors 301

11.3.3 Integrated Surface Acoustic Wave and Photoconductive Wireless UV Detectors 305

11.3.4 Photodetectors Using ZnO TFT 314

11.3.5 MgxZn1_xO UV Photodetector 315

11.4 ZnO NW UV Photodetectors 318

11.4.1 Photoconductive Gain in a ZnO NW 318

11.4.2 Noise Characteristics of ZnO NW UV Photodetector 323

11.5 Conclusions 325

Acknowledgements 325

References 326

12 Room-Temperature Stimulated Emission from ZnO Multiple Quantum Wells Grown on Lattice-Matched Substrates 331
Takayuki Makino, Yusaburo Segawa, Masashi Kawasaki and Hideomi Koinuma

12.1 Introduction 331

12.2 Experimental Details 333

12.3 Quantum Confinement Effect of Excitons in QWs 333

12.4 Exciton–Phonon Interaction in QWs 336

12.5 The Localization Mechanism of the Exciton in a QW 337

12.6 Time-Resolved Luminescence in ZnO QWs 341

12.7 Stimulated Emission in MQWs 342

12.8 Summary 346

Acknowledgements 347

References 347

Index 351

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