Woodhead Publishing Series in Electronic and Optical Materials: Number 54 Nitride semiconductor light-emitting diodes (LEDs) Materials, technologies and applications Edited by JianJang Huang, Hao-Chung Kuo and Shyh-Chiang Shen WP WOODHEAD PUBLISHING r^a Oxford Cambridge Philadelphia New Delhi
Contents Contributor contact details Woodhead Publishing Series in Electronic and Optical Materials Preface xiii xvii xxiii Part I Materials and fabrication 1 1 Molecular beam epitaxy (MBE) growth of nitride semiconductors 3 Q.-D. Zhuang, Lancaster University, UK 1.1 Introduction 3 1.2 Molecular beam epitaxial (MBE) growth techniques 4 1.3 Plasma-assisted MBE (PAMBE) growth of nitride epilayers and quantum structures 5 1.4 Nitride nanocolumn (NC) materials 12 1.5 Nitride nanostructures based on NCs 17 1.6 Conclusion 21 1.7 References 21 2 Modern metal-organic chemical vapor deposition (MOCVD) reactors and growing nitride-based materials 27 F. H. Yang, AIXTRON Taiwan Co Ltd, Taiwan 2.1 Introduction 27 2.2 MOCVD systems 28 2.3 Planetary reactors 35 2.4 Close-coupled showerhead (CCS) reactors 45 2.5 In situ monitoring systems and growing nitride-based materials 54 2.6 Acknowledgements 65 2.7 References 65 v
vi Contents 3 Gallium nitride (GaN) on sapphire substrates for visible LEDs 66 J.-H. Ryou, University of Houston, USA 3.1 Introduction 66 3.2 Sapphire substrates 69 3.3 Strained heteroepitaxial growth on sapphire substrates 77 3.4 Epitaxial overgrowth of GaN on sapphire substrates 81 3.5 GaN growth on non-polar and semi-polar surfaces 86 3.6 Future trends 88 3.7 References 89 4 Gallium nitride (GaN) on silicon substrates for LEDs 99 M. H. Kane, Texas A & M University at Galveston, USA and N. Arefin, University of Oklahoma, USA 4.1 Introduction 99 4.2 An overview of gallium nitride (GaN) on silicon substrates 100 4.3 Silicon overview 101 4.4 Challenges for the growth of GaN on silicon substrates 104 4.5 Buffer-layer strategies 105 4.6 Device technologies 113 4.7 Conclusion 139 4.8 References 139 5 Phosphors for white LEDs 144 H. Yamamoto, formerly of Tokyo University of Technology, Japan and T. Yamamoto, Ajinomoto Pharmaceuticals Co, Ltd, Japan 5.1 Introduction 144 5.2 Optical transitions of Ce3+and Eu2+ 146 5.3 Chemical composition of representative nitride and oxynitride phosphors 149 5.4 Compounds activated by Eu2+ 150 5.5 Compounds activated by Ce3+ 165 5.6 Features of the crystal structure of nitride and oxynitride phosphors 168 5.7 Features of optical transitions of nitride and oxynitride phosphors 171 5.8 Conclusion and future trends 175 5.9 Acknowledgements 176 5.10 References 176 6 Fabrication of nitride LEDs 181 R.-H. Horng, D.-S. Wuu and C.-F. Lin, National Chung Hsing University, Taiwan and C.-F. Lai, Feng-Chia University, Taiwan 6.1 Introduction 181
Contents vii 6.2 GaN-based flip-chip LEDs and flip-chip technology 183 6.3 GaN FCLEDs with textured micro-pillar arrays 185 6.4 GaN FCLEDs with a geometric sapphire shaping structure 191 6.5 GaN thin-film photonic crystal (PC) LEDs 198 6.6 PC nano-structures and PC LEDs 200 6.7 Light emission characteristics of GaN PC TFLEDs 205 6.8 Conclusion 211 6.9 References 212 7 Nanostructured LEDs 216 C. -C. Lin, D. W. Lin, C.-H. Chiu, Z. Y. Li and Y. P. Lan, National Chiao Tung University, Taiwan, J. J. Huang, National Taiwan University, Taiwan and H.-C. Kuo, National Chiao Tung University, Taiwan 7.1 Introduction 216 7.2 General mechanisms for growth of gallium nitride (GaN) related materials 218 7.3 General characterization method 223 7.4 Top-down technique for nanostructured LEDs 225 7.5 Bottom-up technique for GaN nanopillar substrates prepared by molecular beam epitaxy 240 7.6 Conclusion 245 7.7 References 245 8 Nonpolar and semipolar LEDs 250 Y.-R. Wu, National Taiwan University, Taiwan, C.-Y. Huang, TSMC Solid State Lighting, Ltd, Taiwan, and Y. Zhao and J. S. Speck, University of California, Santa Barbara, USA 8.1 Motivation: limitations of conventional c-plane LEDs 250 8.2 Introduction to selected nonpolar and semipolar planes 255 8.3 Challenges in nonpolar and semipolar epitaxial growth 263 8.4 Light extraction for nonpolar and semipolar LEDs 267 8.5 References 270 Part II Performance of nitride LEDs 277 9 Efficiency droop in gallium indium nitride (GalnN)/gallium nitride (GaN) LEDs 279 D. S. Meyaard, G.-B. Lin, J. Cho and E. F. Schubert, Rensselaer Polytechnic Institute, USA 9.1 Introduction 279 9.2 Recombination models in LEDs 281 9.3 Thermal roll-over in gallium indium nitride (GalnN) LEDs 282 9.4 Auger recombination 284
viii Contents 9.5 High-level injection and the asymmetry of carrier concentration and mobility 286 9.6 Non-capture of carriers 290 9.7 Polarization fields 291 9.8 Carrier derealization 291 9.9 Discussion and comparison of droop mechanisms 293 9.10 Methods for overcoming droop 294 9.11 References 298 10 Photonic crystal nitride LEDs 301 M. D. B. Charlton, University of Southampton, UK 10.1 Introduction 301 10.2 Photonic crystal (PC) technology 310 10.3 Improving LED extraction efficiency through PC surface patterning 318 10.4 PC-enhanced light extraction in P-side up LEDs 322 10.5 Modelling PC-LEDs 326 10.6 P-side up PC-LED performance 335 10.7 PC-enhanced light extraction in N-side up LEDs 342 10.8 Summary 350 10.9 Conclusions 352 10.10 References 353 11 Surface plasmon enhanced LEDs 355 Q. Hao and T. Qiu, Southeast University, China and P. K. Chu, City University of Hong Kong, China 11.1 Introduction 355 11.2 Mechanism for plasmon-coupled emission 356 11.3 Fabrication of plasmon-coupled nanostructures 358 11.4 Performance and outlook 363 11.5 Acknowledgements 365 11.6 References 365 12 Nitride LEDs based on quantum wells and quantum dots 368 J. Verma, A. Verma, V. Protasenko, S. M. Islam and D. Jena, University of Notre Dame, USA 12.1 Light-emitting diodes (LEDs) 368 12.2 Polarization effects in IH-nitride LEDs 379 12.3 Current status of Ill-nitride LEDs 390 12.4 Modern LED designs and enhancements 399 12.5 References 400
Contents ix 13 Color tunable LEDs 409 Y. F. Cheung, Z. Ma and H. W. Choi, The University of Hong Kong, People's Republic of China 13.1 Introduction 409 13.2 Initial idea for stacked LEDs 410 13.3 Second-generation LED stack with inclined sidewalls 412 13.4 Third-generation tightly-integrated chip-stacking approach 417 13.5 Group-addressable pixelated micro-led arrays 423 13.6 Conclusions 426 13.7 References 427 14 Reliability of nitride LEDs 428 T.-T. Chen, C.-F. Dai, C.-P. Wang, H.-K. Fu, P.-T. Chou and W. Y. Yeh, Industrial Technology Research Institute (ITRI), Taiwan 14.1 Introduction 428 14.2 Reliability testing of nitride LEDs 428 14.3 Evaluation of LED degradation 431 14.4 Degradation mechanisms 434 14.5 Conclusion 439 14.6 References 440 15 Chip packaging: encapsulation of nitride LEDs 441 X. Luo and R. Hu, Huazhong University of Science and Technology, People's Republic of China 15.1 Functions of LED chip packaging 441 15.2 Basic structure of LED packaging modules 446 15.3 Processes used in LED packaging 449 15.4 Optical effects of gold wire bonding 453 15.5 Optical effects of phosphor coating 456 15.6 Optical effects of freeform lenses 463 15.7 Thermal design and processing of LED packaging 468 15.8 Conclusion 476 15.9 References 476 Part III Applications of nitride LEDs 483 16 White LEDs for lighting applications: the role of standards 485 R. Kotschenreuther, OSRAM GmbH, Germany 16.1 General lighting applications 485 16.2 LED terminology 487 16.3 Copying traditional lamps? 490
x Contents 16.4 Freedom ofchoice 491 16.5 Current and future trends 494 16.6 References 495 17 Ultraviolet LEDs 497 H. Hirayama, RIKEN, Japan 17.1 Research background of deep ultraviolet (DUV) LEDs 497 17.2 Growth of low threading dislocation density (TDD) A1N layers on sapphire 502 17.3 Marked increases in internal quantum efficiency (IQE) 507 17.4 Aluminum gallium nitride (AlGaN)-based DUV-LEDs fabricated on high-quality aluminum nitride (A1N) 513 17.5 Increase in electron injection efficiency (EIE) and light extraction efficiency (LEE) 521 17.6 Conclusions and future trends 528 17.7 References 530 18 Infrared emitters made from Ill-nitride semiconductors 533 Y. Kotsar and E. Monroy, CEA-Grenoble, INAC/SP2M/NPSC, France 18.1 Introduction 533 18.2 High indium (In) content alloys for infrared emitters 534 18.3 Rare-earth (RE) doped gallium nitride (GaN) emitters 536 18.4 Ill-nitride materials for intersubband (ISB) optoelectronics 538 18.5 ISB devices 549 18.6 Conclusions 556 18.7 Acknowledgements 557 18.8 References 557 19 LEDs for liquid crystal display (LCD) backlighting 566 C.-F. Chen, National Central University, Taiwan 19.1 Introduction 566 19.2 Types of LED LCD backlighting units (BLUs) 567 19.3 Technical considerations for optical films and plates 571 19.4 Requirements for LCD BLUs 572 19.5 Advantages and history of LED BLUs 574 19.6 Market trends and technological developments 577 19.7 Optical design 583 19.8 References 593 20 LEDs in automotive lighting 595 J. D. Bullough, Rensselaer Polytechnic Institute, USA 20.1 Introduction 595
Contents xi 20.2 Forward lighting 595 20.3 Signal lighting 599 20.4 Human factor issues with LEDs 599 20.5 Energy and environmental issues 603 20.6 Future trends 603 20.7 Sources offurther information and advice 604 20.8 Acknowledgments 604 20.9 References 604 Index 607