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

Tae-Yeon Seong received his PhD from the University of Oxford in 1992. He is currently 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, developing these materials for illumination applications, and the development of oxide-based and nanomaterials-based transparent conducting oxides for LEDs and OLEDs. He has authored and coauthored over 410 papers in peer-reviewed journals and holds 200 patents (registered and pending). He is a Fellow of the Institute of Physics (UK) and SPIE (The International Society for Optics and Photonics), an Associate Editor of Semiconductor Science and Technology, and an Editorial Advisory Committee Member of the Electrochemical Society Journals. Jung Han is the William Norton Professor in Technological Innovation and a Professor of Electrical Engineering at Yale University. Professor Han’s current research activities include blue, green, and ultraviolet (UV) light emitting devices for energy-efficient solid-state lighting, synthesis of AlGaInN nanostructures, nanoscale phenomena in crystal growth, and AlGaInN photonic devices. He has published more than 250 papers in peer-reviewed journals gathering more than 9,000 citations, and has served as editor of four books and special journal issues. He holds ten U.S. patents and is the co-founder of Saphlux, a startup company based on his inventions for semipolar GaN LEDs. Prof. Han has received numerous awards including a Department of Commerce R&D 100 Award, MRS Ribbon Award, and EMC Best Paper Award. Han is a member of the Connecticut Academy of Science and Engineering, and a Fellow of the Institute of Physics (IoP) and the Institute of Electrical and Electronic Engineers (IEEE).Hiroshi Amano received D.Eng from Nagoya University in 1989. Currently he is a Director, Center for Integrated Research of Future Electronics, and a Professor, Institute of Materials and Systems for Sustainability, 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 525 technical papers and contributed to 27 books. Awards received include: 1994 Optoelectronics Conference Special Award, 1996 IEEE/LEOS Engineering Achievement Award, 1998 Japan Society for Applied Physics C Award, 1998 Rank Award, 2001 Marubun Academic Award, 2002 Takeda Award, 2003 SSDM paper award, Fellow of Japan Society of Applied Physics, NISTEP Award, IOP Fellow, 2014 Nobel Prize in Physics, and Order of Culture, Japan..Hadis Morkoç received Ph.D. from Cornell University, Ithaca, 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, Fellow of APS, was Life Fellow of 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.

Contents 1
Contributors 1
1 Progress and Prospect of Growth of Wide-Band-Gap Group III Nitrides 12
1.1 History of III–V Research (1950s–1970s) 12
1.2 Dawn of GaN Research (1970s to Mid-1980s) 14
1.3 Low-Temperature-Deposited Buffer Layer, p-Type GaN and Highly Luminescent InGaN (Late 1980s) 15
1.4 Summary 19
Acknowledgements 19
References 20
2 Ultra-Efficient Solid-State Lighting: Likely Characteristics, Economic Benefits, Technological Approaches 21
Abstract 21
2.1 Some Likely Characteristics of Ultra-efficient ( greaterthan 70%) SSL 22
2.2 The Ultimate SSL Source is Spiky 24
2.2.1 Spiky Spectra Give Good CRI 24
2.2.2 Spiky Spectra Give the Highest MWLERs 26
2.3 Economic Benefits of Ultra-Efficient SSL 27
2.3.1 Scenario 1: Light Is not a Factor of Production 27
2.3.2 Scenario 2: Light is a Factor of Production 29
2.3.3 A Qualified Nod to Scenario 2: More Light = More Productivity 29
2.4 Two Competing Approaches: Low- and High-Power Densities 30
2.4.1 Low-Power-Density Approach (LEDs) 31
2.4.2 High-Power-Density Approach 34
2.5 Summary 36
Acknowledgements 36
References 36
3 LEDs Based on Heteroepitaxial GaN on Si Substrates 39
3.1 Introduction 39
3.2 Epitaxial Growth and Characterization 42
3.2.1 GaN Growth on Sapphire 42
3.2.2 GaN Growth on SiC 50
3.2.3 GaN/Si Using Low Temperature (LT) Intermediate Layers 50
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) 52
3.2.6 GaN/Si Using SLS Interlayers 53
3.2.7 Recent Progress of the Growth of GaN/Si 56
3.2.8 Other Epitaxial Growth Methods 58
3.3 Fabrication of LEDs and Their Performances 58
3.3.1 Device Characteristics of LED Structures with HT-AlN/AlGaN Intermediate Layers [75–79] 58
3.3.2 Effect of Thin AlN Intermediate Layers and AlN/GaN MLs [35, 82–89] 59
3.3.3 Wafer Bonding and Lift-Off [90] 63
3.3.4 Effect of the Insertion of SLS Layers [110–112] 66
3.3.5 Other Structures 68
3.4 Conclusion 71
Acknowledgements 71
References 71
4 Epitaxial Growth of GaN on Patterned Sapphire Substrates 78
Abstract 78
4.1 Introduction 78
4.2 Properties and Fabrication of PSSs 79
4.3 Growth of GaN on PSS, and Properties of GaN-LEDs on PSS 81
4.3.1 SAG and ELO 81
4.3.2 GaN Growth on PSS and the Mechanism of Decreasing Dislocation Density by ELO 84
4.3.3 Characteristics of LEDs Grown on PSS 87
4.4 The Principle of Light Extraction Efficiency Improvement of GaN-Based LEDs by Patterned Sapphire Substrate 87
4.4.1 Impact of Surface Structure of LEDs on Light Extraction Efficiency Improvement 87
4.4.2 The Principle of Light Extraction Efficiency Improvement of GaN-Based LEDs by Patterned Sapphire Substrate 89
4.4.3 Development of PSS with Micrometer-Sized Structures 90
4.4.4 Development of PSS with Sub-micrometer-Sized Structures 91
4.5 Novel Application of PSS to Growth of Nonpolar or Semipolar GaN 95
4.6 Summary 98
References 99
5 Growth and Optical Properties of GaN-Based Non- and Semipolar LEDs 102
5.1 Introduction 102
5.2 Piezoelectric and Spontaneous Polarization in Group-III Nitrides 103
5.3 Growth of GaN and InGaN on Different Non- and Semipolar Surface Orientations 107
5.3.1 Heteroepitaxial Growth of Non- and Semipolar GaN on Sapphire, Silicon, Spinel, and LiAlO2 Substrates 108
5.3.2 Surface Morphologies and Strutural Defects of Non- and Semipolar GaN Films 110
5.3.3 Indium Incorporation in InGaN Layers and Quantum Wells on Different Semipolar and Nonpolar Surfaces 113
5.4 Polarization of the Light Emission from Non- and Semipolar InGaN QWs 114
5.4.1 Light Emission from Nonpolar InGaN QWs 116
5.4.2 Light Emission from Semipolar InGaN QWs 118
5.5 Performance Characteristics of Non- and Semipolar InGaN QW Light Emitting Diodes 123
5.5.1 Wavelength Shift 123
5.5.2 Droop 125
5.5.3 Polarization and Light Extraction 126
5.5.4 3D-semipolar LEDs on C-plane Sapphire 127
5.5.5 State of the Art of Non- and Semipolar Blue, Green, and White LEDs 128
5.5.6 Toward Yellow LEDs and Beyond 129
5.6 Summary and Outlook 130
References 131
6 Internal Quantum Efficiency in Light-Emitting Diodes 138
6.1 Introduction 139
6.2 Assessment of IQE from Photoluminescence Measurements 140
6.3 Principle of IQE Assessment from Electroluminescence Measurements 142
6.3.1 Calculation of Light Extraction Efficiency in a Simple GaN-Based LED 145
6.3.2 Application to LEDs Grown on Bulk GaN Substrates, Complex LED Structures, and Lasers 147
6.4 Experimental Assessment of IQE 148
6.4.1 IQE Measurement of a State-of-the-Art LED 149
6.4.2 EL-Based IQE Measurement of a Poor-Performing LED: Effect of Surface Roughness 151
6.5 Model for Photon Recycling 153
6.6 Conclusions 154
References 169
7 Internal Quantum Efficiency 171
Abstract 171
7.1 LED Efficiency 171
7.2 Efficiency Droop Mechanisms 174
7.2.1 Efficiency Droop Overview 174
7.2.2 Auger Nonradiative Recombination 177
7.2.3 Defect-Related Nonradiative Recombination 178
7.2.4 Transport-Related Nonradiative Recombination 179
7.2.5 Saturated Radiative Recombination 181
7.2.6 Comprehensive Efficiency Droop Model 184
7.3 IQE Measurement Methods 189
7.3.1 Constant ABC Model 191
7.3.2 Temperature-Dependent Photoluminescence (TDPL) Method 195
7.3.3 Intensity-Dependent Photoluminescence (IDPL) Method 199
7.3.4 Temperature-Dependent Time-Resolved Photoluminescence (TD-TRPL) Method 202
7.3.5 Room Temperature Time-Resolved Photoluminescence (RT-TRPL) Method 204
7.4 Conclusion 211
References 212
8 III-Nitride Tunnel Junctions and Their Applications 216
Abstract 216
8.1 Introduction and Motivation 216
8.2 Polarization Engineering for Enhanced Tunneling 220
8.3 MBE-Based GaN Tunnel Junctions 222
8.4 MOCVD-Grown III-Nitride Tunnel Junctions 226
8.4.1 Lateral Mg Activation 227
8.4.2 InGaN-Based Tunnel Junctions 229
8.4.3 Band Engineering: Graded Layers 232
8.5 Device Realization Utilizing Tunnel Junctions 234
8.5.1 Tandem Structures 234
8.5.2 Current Confinement Structures 235
8.5.3 Simple Device Fabrications 238
8.6 AlGaN-Based Tunnel Junctions for UV LEDs 240
8.7 Summary and Future Directions 241
Acknowledgements 242
References 242
9 Green, Yellow, and Red LEDs 246
Abstract 246
9.1 Introduction 246
9.2 The “Green Gap” 247
9.2.1 Phosphor-Conversion LEDs and Color-Mixing RGB LEDs 247
9.2.2 Obstacles in InGaN Systems with High Indium Content 249
9.3 Growth of InGaN Films with High Indium Content 250
9.3.1 Immiscibility of Indium Incorporation into GaN 250
9.3.2 Growth of MQWs at High Temperatures and High Growth Rates 252
9.4 Local Structure in MQWs 255
9.4.1 Effect of Thin AlGaN Capping IL onto Each QW Layer 255
9.4.2 Effect of Short-Period InGaN/GaN Barrier Layer 257
9.5 Device Performance and Characteristics 261
9.5.1 Device Structure 261
9.5.2 Dependence of Characteristics on Wavelength 262
9.5.3 Temperature Dependence 266
9.5.4 Phosphor-Free Single White LED Using Multi-wavelength MQW 268
9.5.5 Stacked White LED Without Phosphors 270
References 271
10 AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes 274
Abstract 274
10.1 Introduction 274
10.2 Research Background of DUV LEDs 275
10.3 Growth of High-Quality AlN on Sapphire Substrate 279
10.4 Increase in Internal Quantum Efficiency (IQE) 282
10.5 222–351 nm AlGaN and InAlGaN DUV LEDs 287
10.6 Increase in Electron Injection Efficiency (EIE) by MQB 292
10.7 Future LED Design for High-Light Extraction Efficiency (LEE) 298
10.8 Summary 305
References 305
11 Ray Tracing for Light Extraction Efficiency (LEE) Modeling in Nitride LEDs 307
Abstract 307
11.1 Introduction 308
11.2 Background on Ray Optics 309
11.2.1 Snell-Descartes Law 309
11.2.2 Fresnel Coefficients 310
11.2.3 Modeling with a Ray Optics Approach 311
11.3 The Issue of LEE in GaN-Based LEDs 312
11.4 Ray Propagation and Absorption in Layered Structures 314
11.4.1 Localized Versus Distributed Loss Sources 315
11.4.2 Material Absorption 315
11.4.3 Quantum Well Absorption and Photon Recycling 316
11.4.4 Metal Losses: Mirrors and Contacts 316
11.5 Extraction Strategies and Considerations 317
11.5.1 Index Matching and Guided Modes 317
11.5.2 The Effect of Surface or Interface Texturing 318
11.5.3 Limit to the Ray Tracing Method 320
11.5.4 Sidewall Extraction and Chip Shaping 320
11.6 Simulation of Real LEDs 322
11.6.1 GaN-on-GaN Chip Simulations 324
11.6.2 Effects of Propagation in the GaN Substrate 324
11.6.3 Roughening Interaction with Backside Mirror 326
11.6.4 Angled Sidewalls 327
11.6.5 Impact of Current Spreading Layers 328
11.6.6 Patterned Sapphire Substrate (PSS) 328
11.6.7 Propagation of Light in the Substrate and Active Region for PSS Chips 329
11.6.8 Effect of the Patterning the Sapphire Substrate 330
11.6.9 Flip Chip LEDs 331
11.6.10 Index Effects 333
11.7 Conclusions 334
Acknowledgements 335
Appendix A 335
Discussion of the Origins of the Effects of Surface Roughness and of Sapphire Patterning 335
Appendix B 343
Comparison of Roughening and Angled Sidewalls for GaN Substrate LEDs 343
Appendix C 344
Simulations of Periodic “Rough” Surfaces Versus Random Rough Surfaces 344
References 345
12 Light Extraction of High-Efficient Light-Emitting Diodes 347
Abstract 347
12.1 High Extraction Efficiency Structures 347
12.1.1 Enhanced Light Extraction for GaN LEDs Using Surface Shaping 347
12.1.2 Textured Surfaces for High Extraction 350
12.1.3 Patterned Sapphire Substrate 351
12.1.4 High-Power Vertical-Type LEDs 352
12.1.5 Wafer-Bonding and Electroplating Techniques 354
12.1.6 Chemical Lift-Off 355
12.1.7 n-Type Contacts 356
12.1.8 Randomly Roughened Structure for VLEDs 357
12.1.9 Photonic Crystal Structure 358
12.1.10 High-Power Flip-Chip LEDs 359
References 364
13 Electrical Properties, Reliability Issues, and ESD Robustness of InGaN-Based LEDs 368
13.1 Current–Voltage Characteristics 368
13.2 The Ideality Factor of GaN-Based LEDs 373
13.3 Current Conduction in Reverse-Bias 376
13.4 Degradation of LEDs 378
13.5 Degradation of the Blue Semiconductor Chip Activated by Current 380
13.6 Degradation of the Blue Semiconductor Chip Activated by Temperature 386
13.7 Degradation of the Package/Phosphor System 388
13.8 ESD Failure of GaN-Based LEDs 393
13.9 Conclusions 396
References 397
14 Phosphors and White LED Packaging 401
Abstract 401
14.1 Introduction 401
14.2 Phosphor Materials for White LEDs 403
14.2.1 Selection Criteria of Phosphors 403
14.2.2 Selection of Host Crystals and Activators 404
14.2.3 Type of Phosphors 405
14.2.3.1 Garnets 406
14.2.3.2 Alkaline Earth Orthosilicates 408
14.2.3.3 Alkaline Earth Sulfides/Thiogallates 411
14.2.3.4 (Oxo)nitridosilicates 411
14.3 Color Issues and Luminous Efficacy of White LEDs 416
14.3.1 Color Rendering 416
14.3.2 Luminous Efficacy 417
14.3.3 Chromaticity Coordinates and Color Temperature 417
14.4 White LED Packaging 419
14.4.1 Phosphor-in-Cup White LEDs 420
14.4.2 Remote-Phosphor White LEDs 425
14.4.3 Quantum Dots White LEDs 427
14.5 Summary and Perspective 429
References 430
15 High-Voltage LEDs 437
Abstract 437
15.1 Introduction of Assembled HVLED Modules and Single-Chip HVLEDs 437
15.2 Fabrication, Development, and Characteristics of HVLEDs 439
15.2.1 Structure and Fabrication of HVLED Micro-Chip 439
15.2.2 Basic Characteristics and Methods of Measurement for HVLEDs Under AC Operation 442
15.2.3 Light Emission Characteristics of HVLEDs Under AC Operation 443
15.2.4 Design and Characteristics of HVLED Devices 444
15.2.4.1 Anti-parallel HVLED 444
15.2.4.2 Wheatstone Bridge HVLED 445
15.2.4.3 Hybrid HVLED 448
15.2.5 Characteristics of Various HVLEDs and Traditional DCLED 449
15.3 Important Issues on the Applications of HVLEDs 451
15.3.1 Characteristics of and Possible Solutions for Light Flickering 452
15.3.2 Total Harmonic Distortion Limits 453
15.3.3 The Effect of Floating Driving Voltage 454
15.3.4 Safety Considerations of HVLED Encapsulation Structural Design 454
15.3.5 Measurement Techniques for the Optical, Electrical, and Thermal Properties of HVLED Modules 456
15.3.6 Operating Lifetime 458
15.4 Summary 458
References 459
16 Color Quality of White LEDs 460
Abstract 460
16.1 Introduction 460
16.2 Chromaticity 462
16.2.1 Chromaticity Coordinates and Diagrams 462
16.2.2 CCT and Duv 465
16.2.3 Color Differences for Light Source 467
16.3 Color Rendering Characteristics 468
16.3.1 Object Color Evaluation 468
16.3.2 Color Rendering Index 471
16.3.3 Shortcomings of CRI 472
16.3.3.1 CRI Penalizes Preferred Color-Enhancing Lights 473
16.3.3.2 A High CRI Score Does not Guarantee Good Color Quality 474
16.3.3.3 Problem with Duv Shifts 474
16.3.4 Color Quality Beyond CRI 475
16.4 Luminous Efficacy of Radiation 477
16.5 Color Characteristics for Single-Color LEDs 478
16.5.1 Dominant Wavelength {{/usertwo /lambda}}_{{/usertwo d}} 478
16.5.2 Centroid Wavelength {{/usertwo /lambda}}_{{/usertwo c}} 479
16.5.3 Peak Wavelength {{/usertwo /lambda}}_{{/usertwo p}} 480
16.6 Future Considerations on Color Quality for White LED Developments 480
References 482
17 Emerging System Level Applications for LED Technology 484
Abstract 484
17.1 Introduction 484
17.2 Advanced Lighting Systems 485
17.2.1 New Applications in the Field of Human Health and Well-being 487
17.2.2 Illumination with Communication 489
17.2.3 Illumination with Display Capability 491
17.3 Summary 492
Acknowledgements 493
References 493
Index 496
273505_2_En_BookFrontmatter_OnlinePDF.pdf 1
Contents 7
Contributors 9