III-Nitride Ultraviolet Emitters (eBook)

Preface 6
Contents 9
Contributors 16
1 A Brief Review of III-Nitride UV Emitter Technologies and Their Applications 19
Abstract 19
1.1 Background 19
1.2 UV Light Emitters and Their Applications 21
1.3 UV-LEDs---State of the Art and the Challenges Ahead 22
1.4 UV-LEDs---Key Parameters and Device Performance 25
1.5 The Role of Defects on the IQE of UV-LEDs 28
1.6 Current-Injection Efficiency and Operating Voltages of UV-LEDs 30
1.7 Light Extraction from UV-LEDs 31
1.8 Thermal Management and Degradation of UV-LED 32
1.9 Outlook 34
1.10 Summary 35
Acknowledgment 35
References 36
2 Growth and Properties of Bulk AlN Substrates 44
Abstract 44
2.1 Properties and History of AlN Crystals 44
2.2 AlN Bulk Growth by the PVT Method: Theory 46
2.3 AlN Bulk Growth by the PVT Method: Technology 48
2.4 Seeded Growth and Crystal Enlargement 51
2.5 Structural Defects in PVT-Grown AlN Bulk Crystals 53
2.6 Impurities and Resulting Properties of AlN Substrates 55
2.7 Conclusions and Outlook 58
Acknowledgments 59
References 59
3 Vapor Phase Epitaxy of AlGaN Base Layers on Sapphire Substrates for Nitride-Based UV-Light Emitters 64
Abstract 64
3.1 Introduction 64
3.2 Growth of Al(Ga)N Buffer Layers by MOVPE 66
3.3 Techniques for MOVPE of Al(Ga)N Base Layers with Reduced TDD 68
3.4 Growth of AlGaN Layers by HVPE 71
3.4.1 Fundamentals of the HVPE Technique 71
3.4.2 The Choice of Substrate 75
3.4.3 Selected Results from Growth of AlGaN Layers by HVPE 75
3.4.3.1 Lateral Homogeneity 78
3.4.3.2 Use of MOVPE-Grown AlN/Sapphire Templates 80
3.4.3.3 Direct Growth Start in HVPE 80
3.4.3.4 Growth on PSS with Trenches Along /left[ {11/bar{2}0} /right]_{/rm{sapphire}} 83
3.4.3.5 Growth on PSS with Isotropic Motifs 85
3.5 Summary 87
Acknowledgements 87
References 87
4 Growth Techniques of AlN/AlGaN and Development of High-Efficiency Deep-Ultraviolet Light-Emitting Diodes 91
Abstract 91
4.1 Introduction 91
4.2 Research Background of DUV LEDs 92
4.3 Growth Techniques of High-Quality AlN on Sapphire Substrate 97
4.4 Marked Increase in Internal Quantum Efficiency (IQE) 101
4.5 222--351 nm AlGaN and InAlGaN DUV LEDs 106
4.6 Increase in Electron Injection Efficiency (EIE) by MQB 113
4.7 Future LED Design for Obtaining High Light Extraction Efficiency (LEE) 120
4.8 Summary 127
References 128
5 Impacts of Dislocations and Point Defects on the Internal Quantum Efficiency of the Near-Band-Edge Emission in AlGaN-Based DUV Light-Emitting Materials 130
Abstract 130
5.1 Introduction 131
5.2 Experimental Details 133
5.3 Impacts of Impurities and Point Defects on the Near-Band-Edge Luminescence Dynamics of AlN 135
5.4 Effective Radiative Lifetime of the Near-Band-Edge Emission in AlxGa12212xN Films 140
5.5 Impacts of Si-Doping and Resultant Cation Vacancy Formation on the Luminescence Dynamics of the Near-Band-Edge Emission in Al0.6Ga0.4N Films Grown on AlN Templates 142
5.6 Summary 148
Acknowledgments 148
References 148
6 Optical Polarization and Light Extraction from UV LEDs 152
Abstract 152
6.1 Light Extraction from UV LEDs 153
6.2 Optical Polarization 155
6.2.1 Factors Influencing the Light Polarization Switching in AlGaN Layers 158
6.2.1.1 Strain State of the AlGaN Layers 159
6.2.1.2 Quantum Confinement 161
6.2.2 Optical Polarization Dependence on Substrate Orientation 162
6.2.3 Influence of the Optical Polarization on the Light Extraction Efficiency 164
6.3 Concepts for Improved Light Extraction 167
6.3.1 Contact Materials and Design 167
6.3.1.1 Ohmic Contacts for UV LEDs 168
6.3.1.2 Reflectivity of Contact Metals 169
6.3.1.3 Thermal Management and Current Crowding 171
6.3.2 Surface Preparation 172
6.3.2.1 Surface Patterning 172
6.3.2.2 Patterned Substrates 176
6.3.2.3 Plasmonics 178
6.3.3 Packaging 179
References 181
7 Fabrication of High Performance UVC LEDs on Aluminum-Nitride Semiconductor Substrates and Their Potential Application in Point-of-Use Water Disinfection Systems 186
Abstract 186
7.1 Introduction 187
7.1.1 Types of UVC Light Sources 187
7.1.2 What Is UVC Light? 188
7.1.3 How Does Germicidal UV Work 189
7.2 Fabrication of UVC LEDs on AlN Substrates 190
7.3 Leveraging Performance Gains in UVC LEDs for POU Water Disinfection 198
7.3.1 Effect of UVT 198
7.3.2 Design Flexibility 201
7.3.3 Modeling Flow Cells 201
7.3.4 Example Flow Analysis 202
7.3.5 Working with UVC Light 204
References 206
8 AlGaN-Based Ultraviolet Laser Diodes 208
Abstract 208
8.1 Introduction 209
8.2 Growth on Bulk AlN for Highest Material Quality 211
8.2.1 Bulk AlN Substrate 211
8.2.2 Homoepitaxial AlN 212
8.2.3 AlGaN Laser Heterostructure 213
8.2.4 Multiple Quantum Well Active Zone 214
8.3 High Current Capability in High Band Gap AlGaN Materials 216
8.4 High Injection Efficiency at High Current Levels 220
8.5 Optically Pumped UV Lasers 223
8.6 Alternative Concepts for Compact Deep-UV III-N Lasers 226
8.6.1 Electron-Beam Pumped Laser 227
8.6.2 InGaN-Based VECSEL + Second Harmonic Generation 228
8.7 Summary and Conclusion 229
Acknowledgment 229
References 230
9 Solar- and Visible-Blind AlGaN Photodetectors 233
Abstract 233
9.1 Introduction 233
9.2 Basics of Photodetectors 236
9.2.1 Characteristic Parameters and Phenomena 236
9.2.1.1 Optical Properties of Semiconductors 236
9.2.1.2 Quantum Efficiency and Responsivity 238
9.2.1.3 Rise and Fall Times 241
9.2.1.4 Persistent Photoconductivity (PPC) 243
9.2.1.5 Linearity 245
9.2.1.6 Detection Capability 246
9.2.2 Various Types of Semiconductor Photodetectors 246
9.2.2.1 Photoconductor 246
9.2.2.2 Schottky Barrier Photodiode 248
9.2.2.3 Metal--Semiconductor--Metal Photodetector 250
9.2.2.4 p-i-n Photodiode 251
9.2.2.5 Avalanche Photodiode 252
9.2.2.6 Phototube and Photomultiplier Tube 254
9.3 III-Nitrides for Solid-State UV Photodetection 256
9.3.1 AlGaN-Based Photoconductor 258
9.3.2 AlGaN-Based MSM Photodetector 259
9.3.3 AlGaN-Based Schottky Barrier Photodiode 261
9.3.4 AlGaN-Based p-i-n Photodiode 262
9.3.5 AlGaN-Based Avalanche Photodetector 264
9.3.6 AlGaN-Based Photocathode 266
9.3.7 III-Nitride-Based Devices of High Integration Level 268
9.4 Present Status of Wide Bandgap Photodetectors 269
9.5 Summary and Conclusions 271
References 272
10 Ultraviolet Light-Emitting Diodes for Water Disinfection 281
Abstract 281
10.1 Introduction 281
10.2 Basic Principles of UV Disinfection 282
10.2.1 Factors Influencing UV Fluence 285
10.2.2 Modeling and Validation of UV Reactor Performance 287
10.3 Case Study 288
10.3.1 Proposal for an Experimental Setup to Test UV LEDs 289
10.3.2 Test Conditions 292
10.3.2.1 Disinfection Tests Conducted with UV LEDs 292
10.3.2.2 Microbial Data Analysis 294
10.3.2.3 Physicochemical Water Quality 295
10.3.3 Results of Tests Conducted with UV LEDs 296
10.3.3.1 Module Development and Validation 296
10.3.3.2 Comparison of LEDs Emitting at 282 nm and 269 nm 298
10.3.3.3 Flow-Through Tests 300
10.4 Potential of UV LEDs for Water Disinfection 301
Acknowledgments 302
References 302
11 Application of UV Emitters in Dermatological Phototherapy 306
Abstract 306
11.1 Introduction 306
11.2 Sources for UV Phototherapy 307
11.2.1 Natural Sunlight 308
11.2.2 Gas Discharge Lamps 309
11.2.2.1 Mercury Discharge Lamps 309
Low-Pressure Mercury Discharge Fluorescent Lamps 309
Medium- and High-Pressure Mercury Discharge Lamps 309
11.2.2.2 Dielectric Barrier Discharge Lamps 310
11.2.2.3 Electrodeless Excimer Lamps 311
11.2.3 Lasers 311
11.2.4 UV-LEDs 312
11.3 Variants of Dermatological UV Phototherapy 313
11.3.1 Psoralen Plus UVA (PUVA) Therapy 313
11.3.2 Broadband UVB (BB-UVB) Therapy 315
11.3.3 Narrowband UVB (NB-UVB) Therapy 315
11.3.4 UVA-1 Therapy 316
11.3.5 Targeted UV Phototherapy 316
11.3.6 Extracorporeal Photochemotherapy (ECP) 317
11.4 Mechanisms of Action for Major Dermatological Indications 319
11.4.1 Psoriasis 320
11.4.2 Atopic Dermatitis 320
11.4.3 Vitiligo 321
11.4.4 Cutaneous T-Cell Lymphomas 321
11.4.5 Lichen Planus and Alopecia Areata 322
11.4.6 Systemic Sclerosis and Morphoea 322
11.4.7 Graft-Versus-Host Disease 322
11.4.8 Polymorphic Light Eruption 323
11.5 Clinical Studies with Novel UV Emitters 323
11.5.1 Study with an Electrodeless Excimer Lamp 323
11.5.2 Study with UV-LEDs 325
11.6 Summary and Outlook 326
References 327
12 UV Emitters in Gas Sensing Applications 333
Abstract 333
12.1 Introduction 333
12.2 Light Absorption Spectroscopy 336
12.3 Absorption Spectroscopic Systems 341
12.4 Light Sources for UV Spectroscopy 345
12.5 Optical and Electrical Properties of the LEDs for Spectroscopy Application 349
12.6 Application of UV-LED Absorption Spectroscopy 354
12.6.1 Ozone Sensor 354
12.6.2 Ozone Sensor Design 354
12.6.3 Measurement Arrangement 355
12.6.4 Results 355
12.6.5 SO2 and NO2 Sensor 355
12.6.6 Sensor Design for SO2/NO2 Exhaust Gas Sensor 356
12.6.7 Measurement Setup 357
12.7 Conclusion and Outlook 360
References 360
13 UV Fluorescence Detection and Spectroscopy in Chemistry and Life Sciences 362
Abstract 362
13.1 Introduction 362
13.2 Fundamentals and Apparative Aspects of Fluorescence Detection and Spectroscopy 364
13.3 Fluorescence in Lab-Based Instrumental Analysis 370
13.4 Fluorescence Chemical Sensing for Environmental Monitoring and Bioanalytics 372
13.5 Detection of Microorganisms Using Autofluorescence 380
13.6 Fluorescence in Medical Diagnosis of Skin Diseases 385
13.7 Summary and Outlook 389
References 389
14 UV-B Elicitation of Secondary Plant Metabolites 398
Abstract 398
14.1 Nature and Occurrence of Secondary Plant Metabolites 399
14.2 Nutritional Physiology of Secondary Plant Metabolites 400
14.3 Association Between Fruit and Vegetable Consumption and Chronic Diseases 401
14.4 Secondary Plant Metabolites Within the Plant--Environment Interaction 402
14.4.1 UV-B Perception and Signaling in the Plant 402
14.4.2 UV-B as Stressor and Plant Regulator 404
14.5 Structure-Differentiated Response to UV-B 405
14.5.1 Flavonoids and Other Phenolics 406
14.5.2 Glucosinolates 410
14.6 Tailor-Made UV-B Induction of Secondary Plant Metabolites by UV-B LEDs 413
14.6.1 Current State of Research: UV-B Light-Emitting Diodes for Plant Lightning 413
14.6.2 Advantages of UV-B LEDs for Targeted Triggering of Plant Properties 413
14.6.3 Experimental Setup for Targeted Triggering of Plant Properties by UV-B LEDs 415
14.7 Outlook 416
References 417
15 Application of LEDs for UV-Curing 426
Abstract 426
15.1 Introduction 426
15.2 Light Source 428
15.3 Chemistry and Mechanisms 430
15.4 Kinetics 433
15.5 Medical Applications 435
15.6 Coatings, Inks, and Printing 438
15.7 Stereolithography 441
15.8 Conclusion and Outlook 442
References 443
16 Erratum to: Ultraviolet Light-Emitting Diodes for Water Disinfection 446
Erratum to: Chapter 10 in: M. Kneissl and J. Rass (eds.), III-Nitride Ultraviolet Emitters, Springer Series in Materials Science 227, DOI 10.1007/978-3-319-24100-5_10 446
Index 447