Fundamentals of Silicon Carbide Technology
Growth, Characterization, Devices and Applications
IEEE Press Series

A comprehensive introduction and up-to-date reference to SiC power semiconductor devices covering topics from material properties to applications

Based on a number of breakthroughs in SiC material science and fabrication technology in the 1980s and 1990s, the first SiC Schottky barrier diodes (SBDs) were released as commercial products in 2001.  The SiC SBD market has grown significantly since that time, and SBDs are now used in a variety of power systems, particularly switch-mode power supplies and motor controls.  SiC power MOSFETs entered commercial production in 2011, providing rugged, high-efficiency switches for high-frequency power systems.  In this wide-ranging book, the authors draw on their considerable experience to present both an introduction to SiC materials, devices, and applications and an in-depth reference for scientists and engineers working in this fast-moving field.  Fundamentals of Silicon Carbide Technology covers basic properties of SiC materials, processing technology, theory and analysis of practical devices, and an overview of the most important systems applications.  Specifically included are:

• A complete discussion of SiC material properties, bulk crystal growth, epitaxial growth, device fabrication technology, and characterization techniques.
• Device physics and operating equations for Schottky diodes, pin diodes, JBS/MPS diodes, JFETs, MOSFETs, BJTs, IGBTs, and thyristors.
• A survey of power electronics applications, including switch-mode power supplies, motor drives, power converters for electric vehicles, and converters for renewable energy sources.
• Coverage of special applications, including microwave devices, high-temperature electronics, and rugged sensors.
• Fully illustrated throughout, the text is written by recognized experts with over 45 years of combined experience in SiC research and development.

This book is intended for graduate students and researchers in crystal growth, material science, and semiconductor device technology. The book is also useful for design engineers, application engineers, and product managers in areas such as power supplies, converter and inverter design, electric vehicle technology, high-temperature electronics, sensors, and smart grid technology.

About the Authors xi

Preface xiii

1 Introduction 1

1.1 Progress in Electronics 1

1.2 Features and Brief History of Silicon Carbide 3

1.2.1 Early History 3

1.2.2 Innovations in SiC Crystal Growth 4

1.2.3 Promise and Demonstration of SiC Power Devices 5

1.3 Outline of This Book 6

References 6

2 Physical Properties of Silicon Carbide 11

2.1 Crystal Structure 11

2.2 Electrical and Optical Properties 16

2.2.1 Band Structure 16

2.2.2 Optical Absorption Coefficient and Refractive Index 18

2.2.3 Impurity Doping and Carrier Density 20

2.2.4 Mobility 23

2.2.5 Drift Velocity 27

2.2.6 Breakdown Electric Field Strength 28

2.3 Thermal and Mechanical Properties 30

2.3.1 Thermal Conductivity 30

2.3.2 Phonons 31

2.3.3 Hardness and Mechanical Properties 32

2.4 Summary 32

References 33

3 Bulk Growth of Silicon Carbide 39

3.1 Sublimation Growth 39

3.1.1 Phase Diagram of Si-C 39

3.1.2 Basic Phenomena Occurring during the Sublimation (Physical Vapor Transport) Method 39

3.1.3 Modeling and Simulation 44

3.2 Polytype Control in Sublimation Growth 46

3.3 Defect Evolution and Reduction in Sublimation Growth 50

3.3.1 Stacking Faults 50

3.3.2 Micropipe Defects 51

3.3.3 Threading Screw Dislocation 53

3.3.4 Threading Edge Dislocation and Basal Plane Dislocation 54

3.3.5 Defect Reduction 57

3.4 Doping Control in Sublimation Growth 59

3.4.1 Impurity Incorporation 59

3.4.2 n-Type Doping 61

3.4.3 p-Type Doping 61

3.4.4 Semi-Insulating 62

3.5 High-Temperature Chemical Vapor Deposition 64

3.6 Solution Growth 66

3.7 3C-SiC Wafers Grown by Chemical Vapor Deposition 67

3.8 Wafering and Polishing 67

3.9 Summary 69

References 69

4 Epitaxial Growth of Silicon Carbide 75

4.1 Fundamentals of SiC Homoepitaxy 75

4.1.1 Polytype Replication in SiC Epitaxy 75

4.1.2 Theoretical Model of SiC Homoepitaxy 78

4.1.3 Growth Rate and Modeling 83

4.1.4 Surface Morphology and Step Dynamics 87

4.1.5 Reactor Design for SiC Epitaxy 89

4.2 Doping Control in SiC CVD 90

4.2.1 Background Doping 90

4.2.2 n-Type Doping 91

4.2.3 p-Type Doping 92

4.3 Defects in SiC Epitaxial Layers 93

4.3.1 Extended Defects 93

4.3.2 Deep Levels 102

4.4 Fast Homoepitaxy of SiC 105

4.5 SiC Homoepitaxy on Non-standard Planes 107

4.5.1 SiC Homoepitaxy on Nearly On-Axis {0001} 107

4.5.2 SiC Homoepitaxy on Non-basal Planes 108

4.5.3 Embedded Homoepitaxy of SiC 110

4.6 SiC Homoepitaxy by Other Techniques 110

4.7 Heteroepitaxy of 3C-SiC 111

4.7.1 Heteroepitaxial Growth of 3C-SiC on Si 111

4.7.2 Heteroepitaxial Growth of 3C-SiC on Hexagonal SiC 114

4.8 Summary 114

References 115

5 Characterization Techniques and Defects in Silicon Carbide 125

5.1 Characterization Techniques 125

5.1.1 Photoluminescence 126

5.1.2 Raman Scattering 134

5.1.3 Hall Effect and Capacitance–Voltage Measurements 136

5.1.4 Carrier Lifetime Measurements 137

5.1.5 Detection of Extended Defects 142

5.1.6 Detection of Point Defects 150

5.2 Extended Defects in SiC 155

5.2.1 Major Extended Defects in SiC 155

5.2.2 Bipolar Degradation 156

5.2.3 Effects of Extended Defects on SiC Device Performance 161

5.3 Point Defects in SiC 165

5.3.1 Major Deep Levels in SiC 165

5.3.2 Carrier Lifetime Killer 174

5.4 Summary 179

References 180

6 Device Processing of Silicon Carbide 189

6.1 Ion Implantation 189

6.1.1 Selective Doping Techniques 190

6.1.2 Formation of an n-Type Region by Ion Implantation 191

6.1.3 Formation of a p-Type Region by Ion Implantation 197

6.1.4 Formation of a Semi-Insulating Region by Ion Implantation 200

6.1.5 High-Temperature Annealing and Surface Roughening 201

6.1.6 Defect Formation by Ion Implantation and Subsequent Annealing 203

6.2 Etching 208

6.2.1 Reactive Ion Etching 208

6.2.2 High-Temperature Gas Etching 211

6.2.3 Wet Etching 212

6.3 Oxidation and Oxide/SiC Interface Characteristics 212

6.3.1 Oxidation Rate 213

6.3.2 Dielectric Properties of Oxides 215

6.3.3 Structural and Physical Characterization of Thermal Oxides 217

6.3.4 Electrical Characterization Techniques and Their Limitations 219

6.3.5 Properties of the Oxide/SiC Interface and Their Improvement 234

6.3.6 Interface Properties of Oxide/SiC on Various Faces 241

6.3.7 Mobility-Limiting Factors 244

6.4 Metallization 248

6.4.1 Schottky Contacts on n-Type and p-Type SiC 249

6.4.2 Ohmic Contacts to n-Type and p-Type SiC 255

6.5 Summary 262

References 263

7 Unipolar and Bipolar Power Diodes 277

7.1 Introduction to SiC Power Switching Devices 277

7.1.1 Blocking Voltage 277

7.1.2 Unipolar Power Device Figure of Merit 280

7.1.3 Bipolar Power Device Figure of Merit 281

7.2 Schottky Barrier Diodes (SBDs) 282

7.3 pn and pin Junction Diodes 286

7.3.1 High-Level Injection and the Ambipolar Diffusion Equation 288

7.3.2 Carrier Densities in the “i” Region 290

7.3.3 Potential Drop across the “i” Region 292

7.3.4 Current–Voltage Relationship 293

7.4 Junction-Barrier Schottky (JBS) and Merged pin-Schottky (MPS) Diodes 296

References 300

8 Unipolar Power Switching Devices 301

8.1 Junction Field-Effect Transistors (JFETs) 301

8.1.1 Pinch-Off Voltage 302

8.1.2 Current–Voltage Relationship 303

8.1.3 Saturation Drain Voltage 304

8.1.4 Specific On-Resistance 305

8.1.5 Enhancement-Mode and Depletion-Mode Operation 308

8.1.6 Power JFET Implementations 311

8.2 Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) 312

8.2.1 Review of MOS Electrostatics 312

8.2.2 MOS Electrostatics with Split Quasi-Fermi Levels 315

8.2.3 MOSFET Current–Voltage Relationship 316

8.2.4 Saturation Drain Voltage 319

8.2.5 Specific On-Resistance 319

8.2.6 Power MOSFET Implementations: DMOSFETs and UMOSFETs 320

8.2.7 Advanced DMOSFET Designs 321

8.2.8 Advanced UMOS Designs 324

8.2.9 Threshold Voltage Control 326

8.2.10 Inversion Layer Electron Mobility 329

8.2.11 Oxide Reliability 339

8.2.12 MOSFET Transient Response 342

References 350

9 Bipolar Power Switching Devices 353

9.1 Bipolar Junction Transistors (BJTs) 353

9.1.1 Internal Currents 353

9.1.2 Gain Parameters 355

9.1.3 Terminal Currents 357

9.1.4 Current–Voltage Relationship 359

9.1.5 High-Current Effects in the Collector: Saturation and Quasi-Saturation 360

9.1.6 High-Current Effects in the Base: the Rittner Effect 366

9.1.7 High-Current Effects in the Collector: Second Breakdown and the Kirk Effect 368

9.1.8 Common Emitter Current Gain: Temperature Dependence 370

9.1.9 Common Emitter Current Gain: the Effect of Recombination 371

9.1.10 Blocking Voltage 373

9.2 Insulated-Gate Bipolar Transistors (IGBTs) 373

9.2.1 Current–Voltage Relationship 374

9.2.2 Blocking Voltage 384

9.2.3 Switching Characteristics 385

9.2.4 Temperature Dependence of Parameters 391

9.3 Thyristors 392

9.3.1 Forward Conducting Regime 393

9.3.2 Forward Blocking Regime and Triggering 398

9.3.3 The Turn-On Process 404

9.3.4 dV/dt Triggering 406

9.3.5 The dI/dt Limitation 407

9.3.6 The Turn-Off Process 407

9.3.7 Reverse-Blocking Mode 415

References 415

10 Optimization and Comparison of Power Devices 417

10.1 Blocking Voltage and Edge Terminations for SiC Power Devices 417

10.1.1 Impact Ionization and Avalanche Breakdown 418

10.1.2 Two-Dimensional Field Crowding and Junction Curvature 423

10.1.3 Trench Edge Terminations 424

10.1.4 Beveled Edge Terminations 425

10.1.5 Junction Termination Extensions (JTEs) 427

10.1.6 Floating Field-Ring (FFR) Terminations 429

10.1.7 Multiple-Floating-Zone (MFZ) JTE and Space-Modulated (SM) JTE 432

10.2 Optimum Design of Unipolar Drift Regions 435

10.2.1 Vertical Drift Regions 435

10.2.2 Lateral Drift Regions 438

10.3 Comparison of Device Performance 440

References 443

11 Applications of Silicon Carbide Devices in Power Systems 445

11.1 Introduction to Power Electronic Systems 445

11.2 Basic Power Converter Circuits 446

11.2.1 Line-Frequency Phase-Controlled Rectifiers and Inverters 446

11.2.2 Switch-Mode DC–DC Converters 450

11.2.3 Switch-Mode Inverters 453

11.3 Power Electronics for Motor Drives 458

11.3.1 Introduction to Electric Motors and Motor Drives 458

11.3.2 dc Motor Drives 459

11.3.3 Induction Motor Drives 460

11.3.4 Synchronous Motor Drives 465

11.3.5 Motor Drives for Hybrid and Electric Vehicles 468

11.4 Power Electronics for Renewable Energy 471

11.4.1 Inverters for Photovoltaic Power Sources 471

11.4.2 Converters for Wind Turbine Power Sources 472

11.5 Power Electronics for Switch-Mode Power Supplies 476

11.6 Performance Comparison of SiC and Silicon Power Devices 481

References 486

12 Specialized Silicon Carbide Devices and Applications 487

12.1 Microwave Devices 487

12.1.1 Metal-Semiconductor Field-Effect Transistors (MESFETs) 487

12.1.2 Static Induction Transistors (SITs) 489

12.1.3 Impact Ionization Avalanche Transit-Time (IMPATT) Diodes 496

12.2 High-Temperature Integrated Circuits 497

12.3 Sensors 499

12.3.1 Micro-Electro-Mechanical Sensors (MEMS) 499

12.3.2 Gas Sensors 500

12.3.3 Optical Detectors 504

References 509

Appendix A Incomplete Dopant Ionization in 4H-SiC 511

References 515

Appendix B Properties of the Hyperbolic Functions 517

Appendix C Major Physical Properties of Common SiC Polytypes 521

C. 1 Properties 521

C. 2 Temperature and/or Doping Dependence of Major Physical Properties 522

References 523

Index 525

Tsunenobu Kimoto, Department of Electronic Science and Engineering, Kyoto University, Japan.
Professor Kimoto has been involved in SiC research for more than 20 years and his research activity in this field covers growth, optical and electrical characterization, device processing, device design and fabrication.  He has published more than 300 papers in international journals and has presented more than 50 invited talks at international conferences.  He was a guest editor of the 2008 SiC special issues of IEEE Transactions on Electron Devices. 

James A Cooper, School of Electrical and Computer Engineering, Purdue University, Indiana, USA
Professor Cooper was a member of technical staff at Bell Laboratories for ten years where he was principal designer of AT&T’s first microprocessor and investigated nonlinear transport in silicon inversion layers.  His research at Purdue has centered on semiconductor device physics and characterization, focusing primarily on III-V materials and silicon carbide.  He has co-authored over 250 technical papers and conference presentations.