III-Nitride Based Light Emitting Diodes and Applications (eBook)

Tae-Yeon Seong received his PhD from the University of Oxford. He is a Professor of Materials Science and Engineering and currently Chair of Department of Nanophotonics at Korea University. His research focuses on the area of wide band-gap materials and devices (emitters, detectors and electronics) using GaN and ZnO and developing these materials for illumination applications.  He has authored and coauthored more than 340 peer-reviewed journal papers and holds 130 patents. He is a Fellow of the Institute of Physics (UK) and SPIE, an Associate Editor of Semiconductor Science and Technology, and an Editorial Advisory Committee Member of the Electrochemical Society Journals.Jung Han is a Professor and currently the Chair of Electrical Engineering Department at Yale University. Before joining Yale University in 2001, he was a senior member of technical staff at Sandia National Laboratories, where he established a wide bandgap III-nitride semiconductor research effort for visible and ultraviolet LEDs. His current research activities includes the visible InGaN light emitting structures for energy-efficient solid state lighting, nano-scale synthesis of AlGaInN heterostructures, and hybrid inorganic-organic flexible optoelectronics. He has authored and coauthored more than 200 papers in peer-reviewed journals and holds 7 US patents. He is a fellow of Institute of Physics, UK. The awards he received include MRS Ribbon Award (2005) and R&D 100 (2004).Hiroshi Amano received D.Eng from Nagoya University. He is a Professor at Department of Electrical Engineering and Computer Science, Nagoya University. In 1985, he developed low-temperature deposited buffer layers which provided the technology vendors to the development of high-quality group III semiconductor based LEDs and LDs. In 1989, he succeeded in growing p-type GaN and fabricating p-n junction LEDs for the first time in the world. He has published more than 440 technical papers. The awards he received include: 1996 IEEE/LEOS Engineering Achievement Award, 1998 Japan Society for Applied Physics C Award, 1998 Rank Award, 2001 Marubun Academic Award, and 2002 Takeda Award.Hadis Morkoç received Ph.D. from Cornell University, NY, and Honoris Causa from University of Montpellier II. He held positions at Varian Associates, Palo Alto, CA, University of IL at Urbana-Champaign, AT&T Bell Laboratories, Caltech and JPL, and Air Force Research Laboratories. He is with School of Engineering at VCU, Richmond VA. He is among the most cited with over 1600 publications. He is a Fellow of AAAS, APS and IEEE, and member of Sigma Xi (Life member), Eta Kappa Nu, Phi Kappa Phi (Life member), Sigma Pi Sigma, Tau, Beta Pi, and International Men of Achievement, and ISI highly cited authors.

III-Nitride Based Light Emitting Diodes and Applications 4
Preface 6
Contents 8
Chapter 1: Introduction Part A. Progress and Prospect of Growth of Wide-Band-Gap III-Nitrides 15
1.1 History of III-V Research (1950s to 1970s) 15
1.2 Dawn of GaN Research (1970s to Mid 1980s) 17
1.3 Low-Temperature-Deposited Buffer Layer, p-Type GaN and Highly Luminescent InGaN (Late 1980s) 18
1.4 Summary 22
References 22
Chapter 2: Introduction Part B. Ultra-ef?cient Solid-State Lighting: Likely Characteristics, Economic Bene?ts, Technological Approaches 24
2.1 Some Likely Characteristics of Ultra (> 70 %) Ef?cient SSL
Incandescence 25
PC-LED 25
Discharge 26
100 %-Ef?ciency 26
2.2 The Ultimate SSL Source Is Spiky 27
2.2.1 Spiky Spectra Give Good CRI 27
2.2.2 Spiky Spectra Give the Highest MWLERs 28
2.3 Economic Bene?ts of Ultra-ef?cient SSL 30
2.3.1 Scenario 1: Light Is Not a Factor of Production 30
2.3.2 Scenario 2: Light Is a Factor of Production 31
2.3.3 A Quali?ed Nod to Scenario 2: More Light = More Productivity 32
2.4 Two Competing Approaches: Low and High Power Densities 33
2.4.1 Low Power Density Approach (LEDs) 34
2.4.2 High Power-Density Approach 36
2.5 Summary 37
References 38
Chapter 3: Epitaxy Part A. LEDs Based on Heteroepitaxial GaN on Si Substrates 40
3.1 Introduction 40
3.2 Epitaxial Growth and Characterization 43
3.2.1 GaN Growth on Sapphire 43
3.2.2 GaN Growth on SiC 49
3.2.3 GaN/Si Using Low Temperature (LT) Intermediate Layers 49
3.2.4 GaN/Si Using High Temperature (HT) AlN/AlGaN Intermediate Layers 50
3.2.5 GaN/Si Using HT Intermediate Layers (ILs) and Multilayers (MLs) 51
3.2.6 GaN/Si Using SLS Interlayers 52
3.3 Fabrication of LEDs and Their Performances 56
3.3.1 Device Characteristics of LED Structures with HT AlN/AlGaN Intermediate Layers [62-66] 56
3.3.2 Effect of Thin AlN Intermediate Layers and AlN/GaN MLs [35, 71-78] 57
3.3.3 Wafer Bonding and Lift-Off [79] 60
3.3.4 Effect of the Insertion of SLS Layers [97-99] 63
3.3.5 Other Structures 64
3.4 Conclusion 67
References 67
Chapter 4: Epitaxy Part B. Epitaxial Growth of GaN on Patterned Sapphire Substrates 72
4.1 Introduction 72
4.2 Properties and Fabrication of PSSs 73
4.3 Growth of GaN on PSS, and Properties of GaN-LEDs on PSS 75
4.3.1 SAG and ELO 75
4.3.2 GaN Growth on PSS and the Mechanism of Decreasing Dislocation Density by ELO 78
4.3.3 Characteristics of LEDs Grown on PSS 80
4.4 The Principle of Light Extraction Ef?ciency Improvement of GaN-Based LEDs by Patterned Sapphire Substrate 81
4.4.1 Impact of Surface Structure of LEDs on Light Extraction Ef?ciency Improvement 81
4.4.2 The Principle of Light Extraction Ef?ciency Improvement of GaN-Based LEDs by Patterned Sapphire Substrate 82
4.4.3 Development of PSS with Micrometer-Sized Structures 83
4.4.4 Development of PSS with Sub-micrometer-Sized Structures 85
4.5 Novel Application of PSS to Growth of Nonpolar or Semipolar GaN 88
4.6 Summary 90
References 91
Chapter 5: Growth and Optical Properties of GaN-Based Non- and Semipolar LEDs 95
5.1 Introduction 96
5.2 Piezoelectric and Spontaneous Polarization in Group-III Nitrides 96
5.3 Growth of GaN and InGaN on Different Non- and Semipolar Surface Orientations 100
5.3.1 Heteroepitaxial Growth of Non- and Semipolar GaN on Sapphire, Silicon, Spinel, and LiAlO2 Substrates 101
5.3.2 Surface Morphologies and Strutural Defects of Non- and Semipolar GaN Films 103
5.3.3 Indium Incorporation in InGaN Layers and Quantum Wells on Different Semipolar and Nonpolar Surfaces 106
5.4 Polarization of the Light Emission from Non- and Semipolar InGaN QWs 107
5.4.1 Light Emission from Nonpolar InGaN QWs 110
5.4.2 Light Emission from Semipolar InGaN QWs 111
5.5 Performance Characteristics of Non- and Semipolar InGaN QW Light Emitting Diodes 117
5.5.1 Wavelength Shift 117
5.5.2 Droop 119
5.5.3 Polarization and Light Extraction 120
5.5.4 3D-Semipolar LEDs on c-Plane Sapphire 121
5.5.5 State-of-the-Art of Non- and Semipolar Blue, Green, and White LEDs 121
5.5.6 Towards Yellow LEDs and Beyond 123
5.6 Summary and Outlook 124
References 125
Chapter 6: Active Region Part A. Internal Quantum Ef?ciency in LEDs 132
6.1 Introduction 133
6.2 Assessment of IQE from Photoluminescence Measurements 134
6.3 Principle of IQE Assessment from Electroluminescence Measurements 136
6.3.1 Calculation of Light Extraction Ef?ciency in a Simple GaN-Based LED 139
6.3.2 Application to LEDs Grown on Bulk GaN Substrates, Complex LED Structures and Lasers 141
6.4 Experimental Assessment of IQE 142
6.4.1 IQE Measurement of a State-of-the-Art LED 143
6.4.2 EL-Based IQE Measurement of a Poor Performing LED: Effect of Surface Roughness 145
6.5 Model for Photon Recycling 147
6.6 Conclusions 148
Appendix A: Theoretical Model of Light Emission in LEDs: QW Emission Described by Classical Dipoles 150
A.1 Analytical Model for Light Extraction Ef?ciency 151
A.2 Exact Calculation of the Electric Field in a Multilayer Structure 152
A.3 Model for Light Extraction in a Simple LED Geometry 155
A.4 Determination of the Extraction Ef?ciency: Evaluation of etaextr, eta0extr, Trhom(theta,lambda) and < Tm(0°) >
Appendix B: Sensitivity of Model to LED Parameters 159
Appendix C: Modelling the Angle-Resolved Emission from LEDs: Accounting for Surface Roughness 161
References 162
Chapter 7: Active Region Part B. Internal Quantum Ef?ciency 164
7.1 LED Ef?ciency 164
7.2 Ef?ciency Droop Mechanisms 167
7.2.1 Ef?ciency Droop Overview 167
7.2.2 Auger Nonradiative Recombination 169
7.2.3 Defect-Related Nonradiative Recombination 171
7.2.4 Transport-Related Nonradiative Recombination 172
7.2.5 Saturated Radiative Recombination 173
7.2.6 Comprehensive Ef?ciency Droop Model 177
7.3 IQE Measurement Methods 181
7.3.1 Constant ABC Model 184
7.3.2 Temperature-Dependent Photoluminescence (TDPL) Method 188
7.3.3 Intensity-Dependent Photoluminescence (IDPL) Method 191
7.3.4 Temperature-Dependent Time-Resolved Photoluminescence (TD-TRPL) Method 193
7.3.5 Room-Temperature Time-Resolved Photoluminescence (RT-TRPL) Method 195
7.4 Conclusion 202
References 203
Chapter 8: Electrical Properties, Reliability Issues, and ESD Robustness of InGaN-Based LEDs 207
8.1 Current-Voltage Characteristics 207
8.2 The Ideality Factor of GaN-Based LEDs 212
8.3 Current Conduction in Reverse-Bias 214
8.4 Degradation of LEDs 217
8.5 Degradation of the Blue Semiconductor Chip Activated by Current 218
8.6 Degradation of the Blue Semiconductor Chip Activated by Temperature 224
8.7 Degradation of the Package/Phosphor System 227
8.8 ESD-Failure of GaN-Based LEDs 230
8.9 Conclusions 235
References 235
Chapter 9: Light Extraction Ef?ciency Part A. Ray Tracing for Light Extraction Ef?ciency (LEE) Modeling in Nitride LEDs 240
9.1 Introduction 240
9.2 Background on Ray Optics 241
9.2.1 Snell-Descartes Law 241
9.2.2 Fresnel Coef?cients 242
9.2.3 Modeling with a Ray Optics Approach 243
9.3 The Issue of LEE in GaN-Based LEDs 244
9.4 Ray Propagation and Absorption in Layered Structures 245
9.4.1 Localized vs. Distributed Loss Sources 247
9.4.2 Material Absorption 247
9.4.3 Quantum Well Absorption and Photon Recycling 248
9.4.4 Metal Losses: Mirrors and Contacts 248
9.5 Extraction Strategies and Considerations 249
9.5.1 Index Matching and Guided Modes 249
9.5.2 The Effect of Surface or Interface Texturing 250
9.5.3 Limit to the Ray Tracing Method 251
9.5.4 Sidewall Extraction and Chip Shaping 252
9.6 Simulation of Real LEDs 253
9.6.1 GaN on GaN Chip Simulations 256
9.6.1.1 Effects of Propagation in the GaN Substrate 256
9.6.1.2 Roughening Interaction with Backside Mirror 257
9.6.1.3 Angled Sidewalls 258
9.6.1.4 Impact of Current Spreading Layers 259
9.6.2 Patterned Sapphire Substrate (PSS) 260
9.6.2.1 Propagation of Light in the Substrate and Active Region for PSS Chips 260
9.6.2.2 Effect of the Patterning the Sapphire Substrate 261
9.6.3 Limitations in GaN Chip Dimensions 262
9.6.4 Flip Chip LEDs 263
9.6.5 Index Effects 264
9.7 Conclusions 265
Appendix A: Discussion of the Origins of the Effects of Surface Roughness and of Sapphire Patterning 266
A.1 The Effect of GaN Surface Roughening: Randomization 266
A.2 The Effect of Patterned Sapphire Substrate (PSS) 269
Appendix B: Comparison of Roughening and Angled Sidewalls for GaN Substrate LEDs 274
Appendix C: Simulations of Periodic "Rough" Surfaces vs. Random Rough Surfaces 275
References 276
Chapter 10: Light Extraction Ef?ciency Part B. Light Extraction of High Ef?cient LEDs 279
10.1 Enhanced Light Extraction for GaN LEDs Using Surface Shaping 279
10.2 Textured Surfaces for High Extraction 282
10.3 Patterned Sapphire Substrate 283
10.4 High-Power Vertical-Type LEDs 284
10.5 Wafer Bonding and Electroplating Techniques 286
10.6 Chemical Lift-Off 287
10.7 n-Type Contacts 287
10.8 Randomly Roughened Structure for VLEDs 289
10.9 Photonic Crystal Structure 289
10.10 High Power Flip-Chip LEDs 291
References 296
Chapter 11: Packaging. Phosphors and White LED Packaging 299
11.1 Introduction 299
11.2 Phosphor Materials for White LEDs 301
11.2.1 Selection Criteria of Phosphors 301
11.2.2 Selection of Host Crystals and Activators 302
11.2.3 Type of Phosphors 303
11.2.3.1 Garnets 304
11.2.3.2 Alkaline Earth Orthosilicates 306
11.2.3.3 Alkaline Earth Sul?des/Thiogallates 309
11.2.3.4 (Oxo)nitridosilicates 310
11.3 Color Issues and Luminous Ef?cacy of White LEDs 314
11.3.1 Color Rendering 314
11.3.2 Luminous Ef?cacy 315
11.3.3 Chromaticity Coordinates and Color Temperature 316
11.4 White LED Packaging 318
11.4.1 Phosphor-in-Cup White LEDs 318
11.4.2 Remote-Phosphor White LEDs 322
11.4.3 Quantum Dots White LEDs 325
11.5 Summary and Perspective 327
References 328
Chapter 12: High Voltage LEDs 335
12.1 Introduction of Assembled HVLED Modules and Single-Chip HVLEDs 335
12.2 Fabrication, Development, and Characteristics of HVLEDs 337
12.2.1 Structure and Fabrication of HVLED Micro-Chip 337
12.2.2 Basic Characteristics and Methods of Measurement for HVLEDs Under AC Operation 340
12.2.3 Light Emission Characteristics of HVLEDs Under AC Operation 341
12.2.4 Design and Characteristics of HVLED Devices 342
12.2.4.1 Anti-parallel HVLED 342
12.2.4.2 Wheatstone Bridge HVLED 343
12.2.4.3 Hybrid HVLED 345
12.2.5 Characteristics of Various HVLEDs and Traditional DCLED 346
12.3 Important Issues on the Applications of HVLEDs 348
12.3.1 Characteristics of and Possible Solutions for Light Flickering 349
12.3.2 Total Harmonic Distortion Limits 350
12.3.3 The Effect of Floating Driving Voltage 351
12.3.4 Safety Considerations of HVLED Encapsulation Structural Design 351
12.3.5 Measurement Techniques for the Optical, Electrical, and Thermal Properties of HVLED Modules 353
12.3.6 Operating Lifetime 354
12.4 Summary 355
References 356
Chapter 13: Color Quality of White LEDs 357
13.1 Introduction 357
13.2 Chromaticity 359
13.2.1 Chromaticity Coordinates and Diagrams 359
13.2.2 CCT and Duv 362
13.2.3 Color Differences for Light Source 364
13.3 Color Rendering Characteristics 365
13.3.1 Object Color Evaluation 365
13.3.2 Color Rendering Index 367
13.3.3 Shortcomings of CRI 368
13.3.3.1 CRI Penalizes Preferred Color-Enhancing Lights 369
13.3.3.2 A High CRI Score Does Not Guarantee Good Color Quality 370
13.3.3.3 Problem with Duv Shifts 371
13.3.4 Color Quality Beyond CRI 371
13.4 Luminous Ef?cacy of Radiation 373
13.5 Color Characteristics for Single Color LEDs 374
13.5.1 Dominant Wavelength lambdad 374
13.5.2 Centroid Wavelength lambdac 375
13.5.3 Peak Wavelength lambdap 376
13.6 Future Considerations on Color Quality for White LED Developments 376
References 378
Chapter 14: Emerging System Level Applications for LED Technology 380
14.1 Introduction 380
14.2 Advanced Lighting Systems 381
14.2.1 New Applications in the Field of Human Health and Wellbeing 383
14.2.2 Illumination with Communication 385
14.2.3 Illumination with Display Capability 387
14.3 Summary 388
References 389
Index 391