Zinc Oxide (eBook)

Preface 6
Contents 10
1 Introduction 15
1.1 History of ZnO Research and Contents of This Book 16
1.2 Aim of This Review 18
References 19
2 Crystal Structure, Chemical Binding, and Lattice Properties 21
2.1 Crystal Structure and Chemical Binding 22
2.1.1 ZnO Polytype Structures 22
2.1.2 Phase Transitions 24
2.1.3 Crystal Axis Polarity 24
2.2 Thermal Properties 25
2.2.1 Thermal Expansion Coefficients 25
2.2.2 Specific Heat 26
2.2.3 Thermal Conductivity 27
2.3 The Piezoelectric Effect 28
2.3.1 Principle and Applications 28
2.3.2 The Piezoelectric Tensor 29
2.4 Lattice Dynamics 30
2.4.1 Phonon Symmetry and Eigenvectors of the Wurtzite Lattice 31
2.4.2 Phonon Dispersion Relations 32
2.4.3 Infrared Optical Phonon Spectroscopy 35
2.4.4 Raman Spectroscopy of Phonon Modes 37
2.4.5 Vibration Modes in Doped ZnO 40
2.4.6 Incorporation of Transition Metal Atoms in ZnO 42
2.4.7 Raman Scattering from ZnO Nanoparticles 44
2.5 Phonon–Plasmon Mixed States 45
2.5.1 Collective Charge-Carrier Oscillations 46
2.5.2 Coupling to Polar Longitudinal Phonons 47
References 49
3 Growth 52
3.1 Bulk Growth 53
3.1.1 Vapor Phase Transport 53
3.1.2 Solvothermal Growth 54
3.2 Epitaxial Growth Techniques 55
3.2.1 Metal Organic Chemical Vapor Deposition 59
3.2.2 Molecular Beam Epitaxy 66
3.2.3 Pulsed Laser Deposition 78
3.3 Growth of Self-Organized Nanostructures 79
3.3.1 Growth Techniques for Nano Pillars 80
3.3.2 Properties of Nanopillars 80
References 86
4 Band Structure 90
4.1 The Ordering of the Bands at the Valence Band Maximum in ZnO 90
4.2 ZnO and Its Alloys 97
4.2.1 Cationic Substitution: Mg, Cd, Be in ZnO 98
4.2.2 Anionic Substitution: S, Se in ZnO 102
4.3 Valence and Conduction Band Discontinuities 104
4.3.1 Iso-Valent Hetero-Structures 104
4.3.2 Hetero-Valent Hetero-Structures 105
References 106
5 Electrical Conductivity and Doping 108
5.1 Introduction 108
5.2 Hydrogen in ZnO 110
5.3 Donors in ZnO: Al, Ga, In 111
5.4 Acceptors in ZnO 112
5.5 Mobility 117
5.6 Ohmic and Schottky Contacts on ZnO 118
5.7 Two-Dimensional Electron Gas and Quantum Hall Effect 121
5.8 High-Field Transport and Varistors 123
5.9 Photoconductivity 127
References 130
6 Intrinsic Linear Optical Properties Close to the Fundamental Absorption Edge 133
6.1 Free Excitons in Bulk Samples 133
6.1.1 Free Excitons in Bulk Samples, Epitaxial Layers, and NanoRods 137
6.1.2 Experimental Observations 141
6.2 ZnO-Based Alloys 157
6.3 Surface Exciton Polaritons 162
6.4 Excitons in Structures of Reduced Dimensionality 165
6.4.1 Excitons in Quantum Wells and Superlattices 165
6.4.2 Quantum Wires 167
6.4.3 Quantum Dots 170
6.4.4 Cavity Polaritons 174
References 175
7 Bound Exciton Complexes 181
7.1 ZnO Luminescence: An Overview 181
7.2 Neutral Donor Bound Excitons (A-Valence Band) and Their Two Electron Satellites 184
7.3 Ionized Donor Bound Excitons (A-Valence Band) 189
7.4 A Comparison of the Localization Energies with Theoretical Predictions (the Haynes Rule) 192
7.5 Excited State Properties of the Bound Excitons 195
7.6 Donor–Acceptor Pair Transitions 201
References 209
8 Influence of External Fields 212
8.1 Excitons in Magnetic Fields 212
8.1.1 Zeeman Effect 213
8.1.2 Free and Bound Excitons 214
8.1.2.1 Zeeman Splitting of Neutral Donor and Acceptor Bound Excitons 214
8.1.2.2 Identification of Neutral Donor or Acceptor Bound Excitons 217
8.1.2.3 Zeeman Splitting of Ionized Bound Excitons 218
8.1.2.4 Zeeman Splitting of Free Excitons 220
8.1.3 Selection Rules for Zeeman Splitting of Exciton States in Magnetic Fields 223
8.1.4 Symmetry of Exciton Hole States 224
8.2 Excitons in Strain Fields 226
8.2.1 Uniaxial Pressure 228
8.2.2 Hydrostatic Pressure 230
8.2.3 Biaxial In-Plane Strain 236
References 240
9 Deep Centres in ZnO 244
9.1 The Green and Yellow Emission Bands 244
9.2 Transition Metal Ions 250
9.2.1 ZnO/V 252
9.2.2 ZnO/Fe 255
9.2.3 ZnO/Fe3+ 256
9.2.4 ZnO/Fe2+ 260
9.2.5 ZnO/Co 264
9.2.6 ZnO/Ni 265
9.2.7 ZnO/Cu 269
9.3 Outlook 275
References 275
10 Magnetic Properties 278
10.1 General Overview of the Topic 278
10.2 Short Overview of the Situation in ZnO 280
References 283
11 Nonlinear Optics, High Density Effects and Stimulated Emission 285
11.1 Nonlinear Optics 285
11.2 High Excitation Effects 287
11.2.1 The Intermediate Density Regime 287
11.2.2 Electron–Hole Plasma 292
11.3 Processes for Stimulated Emission 295
11.3.1 Bulk Samples and Epilayers 296
11.3.2 Quantum Wells and Superlattices 303
11.3.3 Nano Rods and Their Cavity Modes 304
11.3.4 Quantum Dots and Random Lasing 306
11.3.5 Cavity Modes, Photonic Crystals and Polariton Lasers 309
References 312
12 Dynamic Processes 317
12.1 Dephasing Dynamics 318
12.2 Relaxation Dynamics 321
12.3 Recombination Dynamics 324
References 330
13 Past, Present and Future Applications 334
13.1 Past Applications 334
13.1.1 The Electro Fax Copy 334
13.1.2 Ferrite Properties 335
13.2 Present and Emerging Applications 335
13.2.1 Cement, Rubber, Paint and Glazes 335
13.2.2 Catalysts, Pharmaceutics, Cosmetics and Food Additives 336
13.2.3 Electronics 336
13.2.4 Gas Sensors 339
13.2.5 TCO, Solar Cells and Some Further Applications 340
13.3 Visions of Future Applications 341
13.3.1 pn Junctions 342
13.3.2 Light Emitting Diodes 343
13.3.3 Field Emitters 347
13.3.4 Spintronics 347
References 348
14 Conclusion and Outlook 355
14.1 Conclusions 355
14.2 Outlook 356
References 357
Index 358