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Semiconductor Laser Engineering, Reliability and Diagnostics: A Practical Approach to High Power and Single Mode Devices / Edition 1

Semiconductor Laser Engineering, Reliability and Diagnostics: A Practical Approach to High Power and Single Mode Devices / Edition 1

by Peter W. Epperlein
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Product Details

ISBN-13: 9781119990338
Publisher: Wiley
Publication date: 03/18/2013
Pages: 522
Product dimensions: 5.90(w) x 9.10(h) x 1.20(d)

About the Author

Dr. Peter W. Epperlein is Technology Consultant with hisown semiconductor technology consulting businessPwe-PhotonicsElectronics-IssueResolution in the UK. He looks backat a thirty years career in cutting edge photonics and electronicsindustries with focus on emerging technologies, both in global andstart-up companies, including IBM, Hewlett-Packard, AgilentTechnologies, Philips/NXP, Essient Photonics and IBM/JDSU LaserEnterprise. He holds Pre-Dipl. (B.Sc.), Dipl. Phys. (M.Sc.) and Dr.rer. nat. (Ph.D.) degrees in physics, magna cum laude, from theUniversity of Stuttgart, Germany.

Dr. Epperlein is an internationally recognized expert incompound semiconductor and diode laser technologies. He hasaccomplished R&D in many device areas such as semiconductorlasers, LEDs, optical modulators, quantum well devices, resonanttunneling devices, FETs, and superconducting tunnel junctions andintegrated circuits. His pioneering work on sophisticateddiagnostic research has led to many world’s first reports andhas been adopted by other researchers in academia and industry. Heauthored more than seventy peer-reviewed journal papers, publishedmore than ten invention disclosures in the IBM Technical DisclosureBulletin, has served as reviewer of numerous proposals forpublication in technical journals, and has won five IBM ResearchDivision Awards. His key achievements include the design andfabrication of high-power, highly reliable, single mode diodelasers.

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Table of Contents

Preface xix

About the author xxiii


Overview 1

1 Basic diode laser engineering principles 3

Introduction 4

1.1 Brief recapitulation 4

1.1.1 Key features of a diode laser 4 Carrier population inversion 4 Net gain mechanism 6 Optical resonator 9 Transverse vertical confinement 11 Transverse lateral confinement 12

1.1.2 Homojunction diode laser 13

1.1.3 Double-heterostructure diode laser 15

1.1.4 Quantum well diode laser 17 Advantages of quantum well heterostructures for diodelasers 22

Wavelength adjustment and tunability 22

Strained quantum well lasers 23

Optical power supply 25

Temperature characteristics 26

1.1.5 Common compounds for semiconductor lasers 26

1.2 Optical output power – diverse aspects 31

1.2.1 Approaches to high-power diode lasers 31 Edge-emitters 31 Surface-emitters 33

1.2.2 High optical power considerations 35 Laser brightness 36 Laser beam quality factor M2 36 Substrate loading 82 Growth 83

1.4.2 Laser wafer processing 84 Ridge waveguide etching and embedding 84 The p-type electrode 84 Ridge waveguide protection 85 Wafer thinning and the n-type electrode 85 Wafer cleaving; facet passivation and coating; laseroptical inspection; and electrical testing 86

1.4.3 Laser packaging 86 Package formats 87 Device bonding 87 Optical power coupling 89 Device operating temperature control 95 Hermetic sealing 95

References 96

2 Design considerations for high-power single spatial modeoperation 101

Introduction 102

2.1 Basic high-power design approaches 103

2.1.1 Key aspects 103

2.1.2 Output power scaling 104

2.1.3 Transverse vertical waveguides 105 Substrate 105 Layer sequence 107 Materials; layer doping; graded-index layer doping108

Materials 108

Layer doping 113

Layer doping – n-type doping 113

Layer doping – p-type doping 113

Graded-index layer doping 114 Active layer 114

Integrity – spacer layers 114

Integrity – prelayers 115

Integrity – deep levels 115

Quantum wells versus quantum dots 116

Number of quantum wells 119 Fast-axis beam divergence engineering 121

Thin waveguides 122

Broad waveguides and decoupled confinement heterostructures122

Low refractive index mode puller layers 124

Optical traps and asymmetric waveguide structures 126

Spread index or passive waveguides 127

Leaky waveguides 128

Spot-size converters 128

Photonic bandgap crystal 130 Stability of the fundamental transverse vertical mode133

2.1.4 Narrow-stripe weakly index-guided transverse lateralwaveguides 134 Ridge waveguide 134 Quantum well intermixing 135 Weakly index-guided buried stripe 137 Slab-coupled waveguide 138 Anti-resonant reflecting optical waveguide 140 Stability of the fundamental transverse lateral mode141

2.1.5 Thermal management 144

2.1.6 Catastrophic optical damage elimination 146

2.2 Single spatial mode and kink control 146

2.2.1 Key aspects 146 Single spatial mode conditions 147 Fundamental mode waveguide optimizations 150

Waveguide geometry; internal physical mechanisms 150

Figures of merit 152

Transverse vertical mode expansion; mirror reflectivity; laserlength 153 Higher order lateral mode suppression by selectivelosses 154

Absorptive metal layers 154

Highly resistive regions 156 Higher order lateral mode filtering schemes 157

Curved waveguides 157

Tilted mirrors 158 Beam steering and cavity length dependence of kinks158

Beam-steering kinks 158

Kink versus cavity length dependence 159 Suppression of the filamentation effect 160

2.3 High-power, single spatial mode, narrow ridge waveguidelasers 162

2.3.1 Introduction 162

2.3.2 Selected calculated parameter dependencies 163 Fundamental spatial mode stability regime 163 Slow-axis mode losses 163 Slow-axis near-field spot size 164 Slow-axis far-field angle 166 Transverse lateral index step 167 Fast-axis near-field spot size 167 Fast-axis far-field angle 168 Internal optical loss 170

2.3.3 Selected experimental parameter dependencies 171 Threshold current density versus cladding layercomposition 171 Slope efficiency versus cladding layer composition172 Slope efficiency versus threshold current density172 Threshold current versus slow-axis far-field angle172 Slope efficiency versus slow-axis far-field angle174 Kink-free power versus residual thickness 174

2.4 Selected large-area laser concepts and techniques 176

2.4.1 Introduction 176

2.4.2 Broad-area (BA) lasers 178 Introduction 178 BA lasers with tailored gain profiles 179 BA lasers with Gaussian reflectivity facets 180 BA lasers with lateral grating-confined angledwaveguides 182

2.4.3 Unstable resonator (UR) lasers 183 Introduction 183 Curved-mirror UR lasers 184 UR lasers with continuous lateral index variation187 Quasi-continuous unstable regrown-lens-train resonatorlasers 188

2.4.4 Tapered amplifier lasers 189 Introduction 189 Tapered lasers 189 Monolithic master oscillator power amplifiers 192

2.4.5 Linear laser array structures 194 Introduction 194 Phase-locked coherent linear laser arrays 194 High-power incoherent standard 1 cm laser bars 197

References 201


Overview 211

3 Basic diode laser degradation modes 213

Introduction 213

3.1 Degradation and stability criteria of critical diode lasercharacteristics 214

3.1.1 Optical power; threshold; efficiency; and transverse modes214 Active region degradation 214 Mirror facet degradation 215 Lateral confinement degradation 215 Ohmic contact degradation 216

3.1.2 Lasing wavelength and longitudinal modes 220

3.2 Classification of degradation modes 222

3.2.1 Classification of degradation phenomena by location222 External degradation 222

Mirror degradation 222

Contact degradation 223

Solder degradation 224 Internal degradation 224

Active region degradation and junction degradation 224

3.2.2 Basic degradation mechanisms 225 Rapid degradation 226

Features and causes of rapid degradation 226

Elimination of rapid degradation 229 Gradual degradation 229

Features and causes of gradual degradation 229

Elimination of gradual degradation 230 Sudden degradation 231

Features and causes of sudden degradation 231

Elimination of sudden degradation 233

3.3 Key laser robustness factors 234

References 241

4 Optical strength engineering 245

Introduction 245

4.1 Mirror facet properties – physical origins of failure246

4.2 Mirror facet passivation and protection 249

4.2.1 Scope and effects 249

4.2.2 Facet passivation techniques 250 E2 process 250 Sulfide passivation 251 Reactive material process 252 N2IBE process 252 I-3 process 254 Pulsed UV laser-assisted techniques 255 Hydrogenation and silicon hydride barrier layer process256

4.2.3 Facet protection techniques 258

4.3 Nonabsorbing mirror technologies 259

4.3.1 Concept 259

4.3.2 Window grown on facet 260 ZnSe window layer 260 AlGaInP window layer 260 AlGaAs window layer 261 EMOF process 261 Disordering ordered InGaP 262

4.3.3 Quantum well intermixing processes 262 Concept 262 Impurity-induced disordering 263

Ion implantation and annealing 263

Selective diffusion techniques 265

Ion beam intermixing 266 Impurity-free vacancy disordering 267 Laser-induced disordering 268

4.3.4 Bent waveguide 269

4.4 Further optical strength enhancement approaches 270

4.4.1 Current blocking mirrors and material optimization 270 Current blocking mirrors 270 Material optimization 272

4.4.2 Heat spreader layer; device mounting; and number ofquantum wells 273 Heat spreader and device mounting 273 Number of quantum wells 273

4.4.3 Mode spot widening techniques 274

References 276

5 Basic reliability engineering concepts 281

Introduction 282

5.1 Descriptive reliability statistics 283

5.1.1 Probability density function 283

5.1.2 Cumulative distribution function 283

5.1.3 Reliability function 284

5.1.4 Instantaneous failure rate or hazard rate 285

5.1.5 Cumulative hazard function 285

5.1.6 Average failure rate 286

5.1.7 Failure rate units 286

5.1.8 Bathtub failure rate curve 287

5.2 Failure distribution functions – statistical modelsfor nonrepairable populations 288

5.2.1 Introduction 288

5.2.2 Lognormal distribution 289 Introduction 289 Properties 289 Areas of application 291

5.2.3 Weibull distribution 291 Introduction 291 Properties 292 Areas of application 294

5.2.4 Exponential distribution 294 Introduction 294 Properties 295 Areas of application 297

5.3 Reliability data plotting 298

5.3.1 Life-test data plotting 298 Lognormal distribution 298 Weibull distribution 300 Exponential distribution 303

5.4 Further reliability concepts 306

5.4.1 Data types 306 Time-censored or time-terminated tests 306 Failure-censored or failure-terminated tests 307 Readout time data tests 307

5.4.2 Confidence limits 307

5.4.3 Mean time to failure calculations 309

5.4.4 Reliability estimations 310

5.5 Accelerated reliability testing –physics–statistics models 310

5.5.1 Acceleration relationships 310 Exponential; Weibull; and lognormal distributionacceleration 311

5.5.2 Remarks on acceleration models 312 Arrhenius model 313 Inverse power law 315 Eyring model 316 Other acceleration models 318 Selection of accelerated test conditions 319

5.6 System reliability calculations 320

5.6.1 Introduction 320

5.6.2 Independent elements connected in series 321

5.6.3 Parallel system of independent components 322

References 323

6 Diode laser reliability engineering program 325

Introduction 325

6.1 Reliability test plan 326

6.1.1 Main purpose; motivation; and goals 326

6.1.2 Up-front requirements and activities 327 Functional and reliability specifications 327 Definition of product failures 328 Failure modes, effects, and criticality analysis 328

6.1.3 Relevant parameters for long-term stability andreliability 330

6.1.4 Test preparations and operation 330 Samples; fixtures; and test equipment 330 Sample sizes and test durations 331

6.1.5 Overview of reliability program building blocks 332 Reliability tests and conditions 334 Data collection and master database 334 Data analysis and reporting 335

6.1.6 Development tests 336 Design verification tests 336

Reliability demonstration tests 336

Step stress testing 337 Accelerated life tests 339

Laser chip 339

Laser module 341 Environmental stress testing – laser chip 342

Temperature endurance 342

Mechanical integrity 343

Special tests 344 Environmental stress testing – subcomponents andmodule 344

Temperature endurance 345

Mechanical integrity 346

Special tests 346

6.1.7 Manufacturing tests 348 Functionality tests and burn-in 348 Final reliability verification tests 349

6.2 Reliability growth program 349

6.3 Reliability benefits and costs 350

6.3.1 Types of benefit 350 Optimum reliability-level determination 350 Optimum product burn-in time 350 Effective supplier evaluation 350 Well-founded quality control 350 Optimum warranty costs and period 351 Improved life-cycle cost-effectiveness 351 Promotion of positive image and reputation 351 Increase in customer satisfaction 351 Promotion of sales and future business 351

6.3.2 Reliability–cost tradeoffs 351

References 353


Overview 355

7 Novel diagnostic laser data for active layer materialintegrity; impurity trapping effects; and mirror temperatures361

Introduction 362

7.1 Optical integrity of laser wafer substrates 362

7.1.1 Motivation 362

7.1.2 Experimental details 363

7.1.3 Discussion of wafer photoluminescence (PL) maps 364

7.2 Integrity of laser active layers 366

7.2.1 Motivation 366

7.2.2 Experimental details 367 Radiative transitions 367 The samples 369 Low-temperature PL spectroscopy setup 369

7.2.3 Discussion of quantum well PL spectra 371 Exciton and impurity-related recombinations 371 Dependence on thickness of well and barrier layer373 Prelayers for improving active layer integrity 375

7.3 Deep-level defects at interfaces of active regions 376

7.3.1 Motivation 376

7.3.2 Experimental details 377

7.3.3 Discussion of deep-level transient spectroscopy results382

7.4 Micro-Raman spectroscopy for diode laser diagnostics 386

7.4.1 Motivation 386

7.4.2 Basics of Raman inelastic light scattering 388

7.4.3 Experimental details 391

7.4.4 Raman on standard diode laser facets 394

7.4.5 Raman for facet temperature measurements 395 Typical examples of Stokes- and anti-Stokes Ramanspectra 396 First laser mirror temperatures by Raman 398

7.4.6 Various dependencies of diode laser mirror temperatures401 Laser material 402 Mirror surface treatment 403 Cladding layers; mounting of laser die; heat spreader;and number of active quantum wells 404

References 406

8 Novel diagnostic laser data for mirror facet disorder effects;mechanical stress effects; and facet coating instability 409

Introduction 410

8.1 Diode laser mirror facet studies by Raman 410

8.1.1 Motivation 410

8.1.2 Raman microprobe spectra 410

8.1.3 Possible origins of the 193 cm−1 mode in (Al)GaAs412

8.1.4 Facet disorder – facet temperature –catastrophic optical mirror damage robustness correlations 413

8.2 Local mechanical stress in ridge waveguide diode lasers416

8.2.1 Motivation 416

8.2.2 Measurements – Raman shifts and stress profiles417

8.2.3 Detection of “weak spots” 419 Electron irradiation and electron beam induced current(EBIC) images of diode lasers 419 EBIC – basic concept 421

8.2.4 Stress model experiments 422 Laser bar bending technique and results 422

8.3 Diode laser mirror facet coating structural instability424

8.3.1 Motivation 424

8.3.2 Experimental details 424

8.3.3 Silicon recrystallization by internal power exposure425 Dependence on silicon deposition technique 425 Temperature rises in ion beam- and plasma enhancedchemical vapor-deposited amorphous

silicon coatings 427

8.3.4 Silicon recrystallization by external power exposure– control experiments 428 Effect on optical mode and P/I characteristics 429

References 430

9 Novel diagnostic data for diverse laser temperature effects;dynamic laser degradation effects; and mirror temperature maps433

Introduction 434

9.1 Thermoreflectance microscopy for diode laser diagnostics435

9.1.1 Motivation 435

9.1.2 Concept and signal interpretation 437

9.1.3 Reflectance–temperature change relationship 439

9.1.4 Experimental details 439

9.1.5 Potential perturbation effects on reflectance 441

9.2 Thermoreflectance versus optical spectroscopies 442

9.2.1 General 442

9.2.2 Comparison 442

9.3 Lowest detectable temperature rise 444

9.4 Diode laser mirror temperatures by micro-thermoreflectance445

9.4.1 Motivation 445

9.4.2 Dependence on number of active quantum wells 445

9.4.3 Dependence on heat spreader 446

9.4.4 Dependence on mirror treatment and coating 447

9.4.5 Bent-waveguide nonabsorbing mirror 448

9.5 Diode laser mirror studies by micro-thermoreflectance451

9.5.1 Motivation 451

9.5.2 Real-time temperature-monitored laser degradation 451 Critical temperature to catastrophic optical mirrordamage 451 Development of facet temperature with operation time453 Temperature associated with dark-spot defects in mirrorfacets 454

9.5.3 Local optical probe 455 Threshold and heating distribution within near-fieldspot 455

9.6 Diode laser cavity temperatures by micro-electroluminescence456

9.6.1 Motivation 456

9.6.2 Experimental details – sample and setup 456

9.6.3 Temperature profiles along laser cavity 457

9.7 Diode laser facet temperature – two-dimensionalmapping 460

9.7.1 Motivation 460

9.7.2 Experimental concept 460

9.7.3 First temperature maps ever 460

9.7.4 Independent temperature line scans perpendicular to theactive layer 461

9.7.5 Temperature modeling 462 Modeling procedure 463 Modeling results and discussion 465

References 466

Index 469

What People are Saying About This

From the Publisher

This book represents a well thought description of threefundamental aspects of laser technology: the functioningprinciples, the reliability and the diagnostics. From this point ofview, and, as far as I know, this is a unique example of a bookwhere all these aspects are merged together resulting in awell-balanced presentation. This helps the reader to move with easebetween different concepts since they are presented in a coherentmanner and with the same terminology, symbols and definitions.

The book reads well. It presents the necessary equations andderivations to understand both the physical mechanisms and thepracticalities via a set of useful formulas. In addition, there isthe more important aspect of many real-life examples of how a laseris actually manufactured and which the relevant parameters thatdetermine its behaviour are. It impresses the amounts ofinformation that are given in the book: this would be more typicalof a thick handbook on semiconductor laser than of an agile book.Dr. Epperlein was able to identify the most important concepts andto present them in a clear though concise way.

I am teaching a course on Optoelectronics and I'm going toadvise students to refer to this book, because it has all thenecessary concepts and derivations for a systematic understandingof semiconductor lasers with many worked-out examples, which willhelp the student to grasp the actual problems of designing,manufacturing, testing and using semiconductor lasers. All thevarious concepts are joined to very useful figures, which, ifprovided to instructors as files, can be a useful add-on for theuse of the book as text for teaching. Concepts are always detailedwith numbers to give a feeling of their practical use.

In conclusion, I do find the book suitable for my teachingduties and will refer it to my students.
— Prof. Dr. Lorenzo Pavesi, Head of theDepartment of Physics, University of Trento, Italy, 31 May 2013

Dr. Epperlein has done the semiconductor laser community a greatservice, by releasing the most complete book on the market on thepractical issues of how to make reliable semiconductor lasers.…  

The results are at the cutting edge of our understanding ofsemiconductor laser reliability today, and go well beyond theempirical “black box” approach many use of “tryeverything, and see what works.” The author did a fine job ofpulling together material from many disparate fields. 

Dr. Epperlein has particular expertise in high power single modesemiconductor lasers, and those working on those type of laserswill be especially interested in this book, as there has never beena book published on the fabrication and qualification of suchlasers before. However, those in almost any field of semiconductorlasers will learn items of interest about device design,fabrication, reliability, and characterization. …

This book is written more as a “how to” manual,which should make it more accessible and useful to developmentengineers and researchers in the field.  As with many books ofthis type, it is not necessary to read it from cover-to-cover, itis best skimmed, with deep diving into any areas of specialinterest to the reader. The book is remarkable also, for howcomprehensive it is – even experts will discover somethingnew and useful. 

Dr. Epperlein’s book is an essential read for anyonelooking to develop semiconductor lasers for anything other thanpure research use, and I give it my highest recommendation.
Dr. Robert W. Herrick, Senior Component ReliabilityEngineer, Intel Corp., Santa Clara, CA, USA. July 6, 2013.

The book closes the gap in the current book literature and isthus a unique and excellent example of how to merge design,reliability and diagnostics aspects in a very professional,profound and complete manner. …

All physical and technological principles, concepts andpractical aspects required for developing and fabricatinghighly-reliable high-power single-mode laser products are preciselyspecified and skilfully formulated along with all the necessaryequations, figures, tables and worked-out examples making it easyto follow through the nine chapters.

Hence, this unique book is a milestone in the diode laserliterature and is an excellent reference book for not only diodelaser researchers and engineers, but also diode laser users.…

The book has an elaborate table of contents and index, which arevery useful, over 200 illustrative figures and tables, andextensive lists of references to all technical topics at the end ofeach of the nine chapters, which make it easy to follow from coverto cover or by jumping in at random areas of special interest.Moreover, experimental and theoretical concepts are alwaysillustrated by practical examples and data. ...

I can highly recommend this extremely relevant, well-structuredand well-formulated book to all practising researchers inindustrial and academic diode laser R&D environments and topost-graduate engineering students interested in the actualproblems of designing, manufacturing, testing, characterising andqualifying diode lasers. ...

Due to its completeness and novel approach to combine design,reliability and diagnostics in the same book, it deserves to bewelcomed wordwide by the addressed audience.
Dr. Chung-en Zah, Research Director S&T Division,Corning Inc., Corning NY, USA. June 23, 2013

This book is a landmark in the recent literature onsemiconductor lasers because it fills a longstanding gap betweenmany excellent books on laser theory and the complex andchallenging endeavour to fabricate these devices reproducibly andreliably in an industrial, real world environment. …

I appreciate the competent, complete and skilful presentation ofthe three highly interrelated critical  topics ofstate-of-the-art power laser research - device and mode stabilityengineering, reliability mechanisms/reliability assessmentstrategies and material/device diagnostics all treated with astrong focus on the implementation. This emphasis on the complexpractical aspects for a large-scale power laser fabrication is atrue highlight of the book. …

The subtle interplay between laser design, reliabilitystrategies, advanced failure analysis and characterizationtechniques is elaborated in a very rigorous and scientific wayusing a very clear and easy to read representation of the complexinterrelation of the three major topics. I will concentrate on thenumerous highlights. … The completeness of the presentationon power laser diode design based on basic physical and plausiblearguments is mainly based on analytic mathematical relations aswell as experiments providing a new and well-balanced addition forthe power diode laser literature in particular. …

The novel and really original, “gap-filling” bulk ofthe book is elaborated in a very clear way in the four chapters inpart 2 “Laser Reliability” on laser degradation physicsand mirror design and passivation at high power, followed then bytwo very application oriented chapters on reliability designengineering and practical reliability strategies and implementationprocedures. This original combination of integral design andreliability aspects, which are mostly neglected in standardliterature, is certainly a major plus of this book. I liked part 2as a whole, because it provides excellent insights in degradationphysics on a high level and combines it in an interesting andskilful way with the highly relevant reliability science andtesting strategies, which is particularly important for devicesoperating at extreme optical stresses with challenging lifetimerequirements in a real word environment. …

Part 3 “Laser Diagnostics” … is devoted toadvanced experimental diagnostics techniques for materialintegrity, mechanical stress, deep level defects, various dynamiclaser degradation effects, surface- and interface quality, and mostimportantly heating and disordering of mirrors and mirror coatings.The topics of these techniques … have been pioneered by theauthor for the specific applications over many years guaranteeingmany competent and well- represented insights. These techniques arebrilliantly discussed and the information distributed in manyarticles by the author has been successfully unified in thisbook.

I consider the parts 2 and 3 on reliability and diagnostics asthe most valuable and true novel contribution of the book, which incombination with the extremely well covered laser design of part 1clearly fill the gap in the current diode laser literature, whichin this detail has certainly been neglected in the past.

In summary, I can highly recommend this excellent,well-organized and clearly written book to readers who are alreadyfamiliar with basic diode laser theory and who are active in theacademic and industrial fabrication and characterization ofsemiconductor lasers. Due to its completeness, it also serves as anexcellent reference of the current state-of-the-art in reliabilityengineering and device and material diagnostics.

Needless to mention that the quality of the book, itsrepresentations and methodical structure meet the highestexpectation and are certainly a tribute from the long and broadexperience of the author in academic laser science and theindustrial commercialization of high power diode lasers.

This book was a pleasure to read and due to its quality andrelevance deserves a large audience in the power diode lasercommunity!
Prof. em. Dr. Heinz Jäckel, Swiss FederalInstitute of Technology ETH Zürich, Switzerland. June 16,2013

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