Semiconductor Lasers II Materials and Structures Edited by Eli Kapon Institute of Micro and Optoelectronics Department of Physics Swiss Federal Institute oftechnology, Lausanne OPTICS AND PHOTONICS ACADEMIC PRESS San Diego London Boston New York Sydney Tokyo Toronto
Contents Preface xi Chapter 1 Visible-Wavelength Laser Diodes 1.1 Introduction 1 1.1.1 Relevance of visible wavelength lasers 1 1.1.2 Thermal aspects; the temperature-dependence of threshold current 3 1.1.3 Beam properties, astigmatism 6 1.1.4 High-power operation 7 1.1.5 Organization of this Chapter 7 1.2 Material systems for visible lasers 8 1.2.1 Introduction 8 1.2.2 The InGaAlP material system 8 1.2.3 The MgZnSSe material system 12 1.2.4 The AlInGaN system 14 1.2.5 The chalcopyrites 16 1.3 Epitaxial growth and technology 17 1.3.1 The AlGalnP system 17 1.3.2 The MgZnSSe system 19 1.3.2.1 Introduction 19 1.3.2.2 MBE 20 1.3.2.3 OMVPE 20 1.3.2.4 Ohmic contacts to p-type ZnSe 21 1.3.3 The AlInGaN system 21 1.3.3.1 OMVPE/MOMBE 21 1.3.3.2 Processing and contacting 22 1.4 Quantum wells and strain in laser diodes 22 1.4.1 The effects of quantum wells 22 1.4.2 The effects of strain 25 v
vi Contents 1.5 InGaAlP laser structures 33 1.5.1 Transverse laser structure with bulk InGaP active layer 33 1.5.2 InGaAlP strained layer quantum well lasers 34 1.5.3 Lateral laser structure: gain-guided lasers 39 1.5.4 Electro-optical properties of gain-guided lasers 41 1.5.5 Lateral laser structure: index-guided lasers 42 1.5.6 Electro-optical properties of index-guided lasers 44 1.5.7 High-power operation 44 1.5.8 Laser diode operation at shorter wavelengths (630-650nm) 46 1.5.9 Temperature dependence of the threshold current 48 1.5.10 Reliability of InGaAlP lasers 51 1.6 Short-wavelength visible lasers (blue-green and blue) 55 1.6.1 II VI injection lasers 55 1.6.1.1 Introduction 55 1.6.1.2 The use of CdZnSe strained layer quantum wells and quaternary claddings for blue-green II-VI lasers 55 1.6.1.3 Reliability of II-IV lasers 57 1.6.2 Gallium nitride-based lasers 59 1.7 Conclusions and perspectives toward future developments 62 Acknowledgments 63 References 64 Chapter 2 Long Wavelength (A > 2 /лт) Semiconductor Lasers 2.1 Introduction 71 2.2 Wavelength ranges of various laser materials 73 2.3 Growth techniques 77 2.4 Compounds and alloys of III-V type 82 2.4.1 Brief review of III-V materials for longwavelength laser applications 82 2.4.2 Lasers based on III-V materials 84 2.4.3 Type-II heterojunction InGaSbAs/GaSb 94 2.4.4 InSbAsP/InAs and some other lasers 97 2.5 Compounds and alloys of II-VI type 100 2.5.1 Brief review of II-VI materials for longwavelength laser applications 100
Contents Vll 2.5.2 II-VI-based IR semiconductor laser diodes 102 2.6 Compounds and alloys of IV-VI type 105 2.6.1 Brief review of IV-VI materials for longwavelength laser applications 105 2.6.2 IV-VI-based IR semiconductor laser diodes; comments on history 107 2.6.3 Homojunction laser diodes of IV-VI type 110 2.6.4 Heterojunction laser diodes of IV-VI type 112 2.6.5 Quantum-well IV-VI lasers 114 2.7 Resume of interband laser properties 117 2.7.1 Threshold and power characteristics 117 2.7.2 Mode control and tunability of the laser emission 124 2.7.3 High-temperature operation 127 2.7.4 Longest wavelength of interband semiconductor lasers 129 2.8 Hot-hole (unipolar) semiconductor lasers 130 2.9 Unipolar tunneling-based semiconductor lasers 132 2.9.1 Theoretical schemes of the tunneling pumping 132 2.9.2 Characteristics of quantum cascade lasers 134 2.10 Nonlinear optical conversion in semiconductors 135 2.11 Brief review of applications 136 2.12 Conclusions 140 Acknowledgments 142 References 142 Chapter 3 Single-Mode and Tunable Laser Diodes 3.1 Introduction 157 3.2 Single-mode laser diodes 158 3.2.1 The Fabry-Perot laser diode 158 3.2.2 The distributed Bragg reflector (DBR) laser 164 3.2.2.1 Coupled-mode theory for DBR laser 168 3.2.2.2 Purely passive DBR with nonreflecting end mirror 173 3.2.2.3 Wavelength selectivity of DBR laser 174 3.2.3 Distributed feedback (DFB) laser diodes 179 3.2.3.1 Coupled mode theory for DFB laser 179 3.2.3.2 Spectral linewidth 186 3.2.3.3 Experimental results 189
VUl Contents 3.3 Wavelength tunable laser diodes 193 3.3.1 Physical mechanisms for electronic wavelength tuning in laser diodes 194 3.3.2 Continuously wavelength tunable laser diodes 196 3.3.2.1 Longitudinally integrated structures 200 3.3.2.2 Transversely integrated structures 207 3.3.2.3 Spectral linewidth 214 3.3.2.4 Physical limitations on tuning range of continuously tunable laser diodes 219 3.3.3 Discontinously tunable laser diodes 221 3.3.3.1 DBR-type laser structures 223 3.3.3.2 Wavelength tunable Y-laser 231 3.3.3.3 Codirectionally mode-coupled lasers 238 3.3.3.4 Outlook 249 3.4 Conclusion 250 References 251 Chapter 4 High-Power Semiconductor Lasers 4.1 Introduction 259 4.1.1 Why high power? 260 4.1.2 Power limitations 260 4.1.3 Case study: index-guided single-mode lasers 263 4.2 Beam quality 269 4.2.1 Carrier-induced gain and refractive index 269 4.2.2 The effective index method for finding spatial modes 271 4.2.3 Gain and index waveguiding 277 4.2.4 Filamentation and the a-parameter 278 4.2.5 Brightness, Strehl ratio, and M 2 280 4.2.5.1 Brightness 282 4.2.5.2 Strehl ratio 283 4.2.5.3 M 2 -factor 285 4.2.6 Case study: monolithic flared amplifier master oscillator power amplifier 286 4.3 Thermal management 295 4.3.1 Operating parameters 296 4.3.2 Thermal resistance 302 4.3.3 Characteristic temperature, T 0 304 4.3.4 Reliability and activation energy 305
Contents ix 4.3.5 Case study: QUASI-CW 1 cm-wide laser array bars 308 4.4 Conclusions 318 Acknowledgments 318 References 318 Chapter 5 Surface-Emitting Lasers Abstract 323 5.1 Introduction 323 5.2 Configurations of surface-emitting lasers 325 5.2.1 Categorization of surface-emitting lasers 325 5.2.2 Vertical-cavity surface emitting lasers 326 5.2.3 Grating coupled surface emitting lasers 326 5.2.4 45 Deflecting-mirror surface-emitting lasers 328 5.2.5 Folded cavity semiconductor lasers 328 5.3 Basics of vertical cavity surface-emitting lasers 329 5.3.1 Threshold current and quantum efficiency 329 5.4 Fundamental elements for vertical cavity surfaceemitting lasers 333 5.4.1 Dielectric multilayer mirrors 335 5.4.2 Semiconductor multi-layer structures 335 5.4.3 Quantum wells for gain medium 336 5.4.4 Periodic and matched gain structures 336 5.4.5 Current and optical confinement 336 5.5 Device design and technology 339 5.5.1 Long wavelength surface-emitting lasers 339 5.5.2 GaAlAs/GaAs surface emitting lasers 344 5.5.3 GalnAs/GaAs surface-emitting lasers 346 5.5.4 Short-wavelength surface-emitting lasers 350 5.6 Lasing characteristics of VCSELs 351 5.6.1 Ultimate performances 351 5.6.2 Single-mode behavior 353 5.6.3 Polarization characteristics 354 5.6.4 Quantum noise 356 5.6.5 Spontaneous emission control 356 5.6.6 Photon recycling 357 5.7 Integrations and applied optical subsystems 358 5.7.1 Photonic-stack integration 358 5.7.2 Surface operating devices and monolithic integrations 358
5.8 5.7.3 Two-dimensional arrays of surface-emitting lasers 5.7.4 Applied subsystems Summary References 360 360 364 365 Index 373