Skip to main content

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

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

Peter W. Epperlein

ISBN: 978-1-118-48186-8

Jan 2013

520 pages



This reference book provides a fully integrated novel approach to the development of high-power, single-transverse mode, edge-emitting diode lasers by addressing the complementary topics of device engineering, reliability engineering and device diagnostics in the same book, and thus closes the gap in the current book literature.

Diode laser fundamentals are discussed, followed by an elaborate discussion of problem-oriented design guidelines and techniques, and by a systematic treatment of the origins of laser degradation and a thorough exploration of the engineering means to enhance the optical strength of the laser. Stability criteria of critical laser characteristics and key laser robustness factors are discussed along with clear design considerations in the context of reliability engineering approaches and models, and typical programs for reliability tests and laser product qualifications. Novel, advanced diagnostic methods are reviewed to discuss, for the first time in detail in book literature, performance- and reliability-impacting factors such as temperature, stress and material instabilities.

Further key features include:

  • practical design guidelines that consider also reliability related effects, key laser robustness factors, basic laser fabrication and packaging issues;
  • detailed discussion of diagnostic investigations of diode lasers, the fundamentals of the applied approaches and techniques, many of them pioneered by the author to be fit-for-purpose and novel in the application;
  • systematic insight into laser degradation modes such as catastrophic optical damage, and a wide range of technologies to increase the optical strength of diode lasers;
  • coverage of basic concepts and techniques of laser reliability engineering with details on a standard commercial high power laser reliability test program.

Semiconductor Laser Engineering, Reliability and Diagnostics reflects the extensive expertise of the author in the diode laser field both as a top scientific researcher as well as a key developer of high-power highly reliable devices. With invaluable practical advice, this new reference book is suited to practising researchers in diode laser technologies, and to postgraduate engineering students. 

Dr. Peter W. Epperlein is Technology Consultant with his own semiconductor technology consulting business Pwe-PhotonicsElectronics-IssueResolution in the UK. He looks back at a thirty years career in cutting edge photonics and electronics industries with focus on emerging technologies, both in global and start-up companies, including IBM, Hewlett-Packard, Agilent Technologies, Philips/NXP, Essient Photonics and IBM/JDSU Laser Enterprise. He holds Pre-Dipl. (B.Sc.), Dipl. Phys. (M.Sc.) and Dr. rer. nat. (Ph.D.) degrees in physics, magna cum laude, from the University of Stuttgart, Germany.

Dr. Epperlein is an internationally recognized expert in compound semiconductor and diode laser technologies. He has accomplished R&D in many device areas such as semiconductor lasers, LEDs, optical modulators, quantum well devices, resonant tunneling devices, FETs, and superconducting tunnel junctions and integrated circuits. His pioneering work on sophisticated diagnostic research has led to many world’s first reports and has been adopted by other researchers in academia and industry. He authored more than seventy peer-reviewed journal papers, published more than ten invention disclosures in the IBM Technical Disclosure Bulletin, has served as reviewer of numerous proposals for publication in technical journals, and has won five IBM Research Division Awards. His key achievements include the design and fabrication of high-power, highly reliable, single mode diode lasers.

Book Reviews

“Semiconductor Laser Engineering, Reliability and Diagnostics: A Practical Approach to High Power and Single Mode Devices”. By Peter W. Epperlein

Prof. em. Dr. Heinz Jäckel,
High Speed Electronics and Photonics, Swiss Federal Institute of Technology ETH Zürich, Switzerland

The book “Semiconductor Laser Engineering, Reliability and Diagnostics” by Dr. P.W. Epperlein is a landmark in the recent literature on semiconductor lasers because it fills a longstanding gap between many excellent books on laser theory and the complex and challenging endeavor to fabricate these devices reproducibly and reliably in an industrial, real world environment.

Having worked myself in the early research and development of high power semiconductor lasers, I appreciate the competent, complete and skillful presentation of these three highly interrelated topics, where small effects have dramatic consequences on the success of a final product, on the ultimate performance and on the stringent reliability requirements, which are the name of the game.

As the title suggests the author addresses three tightly interwoven and critical topics of state-of-the-art power laser research. The three parts are: device and mode stability engineering (chapter 1, 2), reliability mechanisms and reliability assessment strategies (chapter 3, 4, 5, 6) and finally material and device diagnostics (chapter 7, 8, 9) all treated with a strong focus on the implementation. This emphasis on the complex practical aspects for a large-scale power laser fabrication is a true highlight of the book.

The subtle interplay between laser design, reliability strategies, advanced failure analysis and characterization techniques are elaborated in a very rigorous and scientific way using a very clear and easy to read representation of the complex interrelation of the three major topics. I will abstain from trying to provide a complete account of all the topics but mainly concentrate on the numerous highlights.

The first part 1 “Laser Engineering” is divided in two chapters on basic electronic-optical, structural, material and resonator laser engineering on the one side, and on single mode control and stability at very high, still reliable power-levels with the trade-off between mirror damage, single mode stability on the other side. To round up the picture less well-known concepts and the state-of-the-art of large-area lasers, which can be forced into single-mode operation, are reviewed carefully. The subtle and complex interplay, which is challenging to optimize for a design for reliability and low stress as a major boundary condition is crucial for the design. The section gives a rather complete and well-referenced account of all relevant aspects, relations and trade-offs for understanding the rest of the book.

The completeness of the presentation on power laser diode design based on basic physical and plausible arguments is mainly based on analytic mathematical relations as well as experiments providing a new and well-balanced addition for the power diode laser literature in particular. Modern 2D self-consistent electro-optical laser modeling including carrier hole burning and thermal effects – this is important because the weak optical guiding and gain-discrimination depend critically on rather small quantities and effects, which are difficult to optimize experimentally – is used in the book for simulation results, but is not treated separately.

The novel and really original, “gap-filling” bulk of the book is elaborated by the author in a very clear way in the following four chapters in the part 2 “Laser Reliability” on laser degradation physics and mirror design and passivation at high power, followed then by two very application oriented chapters on reliability design engineering and practical reliability strategies and implementation procedures. This original combination of integral design and reliability aspects – which are mostly neglected  in standard literature – is certainly a major plus of this book. I liked this second section as a whole, because it provides excellent insights in degradation physics on a high level and combines it in an interesting and skillful way with the less “glamorous” (unfortunately) but highly relevant reliability science and testing strategies, which is particularly important for devices operating at extreme optical stresses with challenging lifetime requirements in a real word environment.

Finally, the last part 3 “Laser Diagnostics” comprising three chapters, is devoted mainly to advanced experimental diagnostics techniques for material integrity, mechanical stress, deep level defects, various dynamic laser degradation effects, surface- and interface quality, and most importantly heating and disordering of mirrors and mirror coatings. The topics of characterization techniques comprising micro-Raman- and micro-thermoreflectance-probing, 2K photoluminescence spectroscopy, micro-electroluminescence and photoluminescence scanning, and deep-level-transient spectroscopy have been pioneered by the author for the specific applications over many years guaranteeing many competent and well represented insights. These techniques are brilliantly discussed and the information distributed in many articles by the author has been successfully unified in a book form.

In my personal judgment and liking, I consider the parts 2 and 3 on reliability and diagnostics as the most valuable and true novel contribution of the book, which in combination with the extremely well-covered laser design of part 1 clearly fill the gap in the current diode laser literature, which in 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 already familiar with basic diode laser theory and who are active in the academic and industrial fabrication and characterization of semiconductor lasers. Due to its completeness, it also serves as an excellent reference of the current state-of-the-art in reliability engineering and device and material diagnostics.

Needless to mention that the quality of the book, its representations and methodical structure meet the highest expectation and are certainly a tribute from the long and broad experience of the author in academic laser science and the industrial commercialization of high power diode lasers.

In my opinion, this book was a pleasure to read and due to its quality and relevance deserves a large audience in the power diode laser community!

Prof. em. Dr. Heinz Jäckel, High Speed Electronics and Photonics, Swiss Federal Institute of Technology ETH Zürich, Switzerland

June 16, 2013


“Semiconductor Laser Engineering, Reliability and Diagnostics: A Practical Approach to High Power and Single Mode Devices”. By Peter W. Epperlein

Dr. Chung-en Zah, Research Director, Semiconductor Technologies Research, S&T Division, Corning Incorporate, Corning NY, USA

This book covers for the first time the three closely interrelated key laser areas of engineering (design), reliability and diagnostics in one book, written by the well-known practitioner in cutting-edge optoelectronics industries, Dr. Peter W. Epperlein. The book closes the gap in the current book literature and is thus 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 and practical aspects required for developing and fabricating highly-reliable high-power single-mode laser products are precisely specified and skilfully formulated along with all the necessary equations, figures, tables and worked-out examples making it easy to follow through the nine chapters. Hence, this unique book is a milestone in the diode laser literature and is an excellent reference book not only for diode laser researchers and engineers, but also diode laser users.

The engineering part starts with a very informative and clear, well-presented account of all necessary basic diode laser types, principles, parameters and characteristics for an easy and quick understanding of laser functionality within the context of the book. Along with an elaborate and broad discussion of relevant laser material systems, applications, typical output powers, power-limiting factors and reliability tradeoffs, basic fabrication and packaging technologies, this excellent introductory section is well suited to become quickly and easily familiar with practical aspects and issues of diode laser technologies. Of special importance and high usefulness is the first analytic and quantitative discussion in a book on issues of coupling laser power into optical single mode fibers. The second section discusses in a well-balanced, competent and skilful way waveguide topics such as basic high-power design approaches, transverse vertical and lateral waveguide concepts, stability of the fundamental transverse lateral mode and fundamental mode waveguide optimization techniques by considering detrimental effects such as heating, carrier injection, spatial hole burning, lateral current spreading and gain profile variations. Less well-known approaches to force large-area lasers into a single mode operation are well-identified and carefully discussed in depth and breadth. All these topics are elaborated in a very complete, rigorous and scientific way and are clearly articulated and easy to read. In particular, the book works out the complex interaction between the many different effects to optimize high-power single-mode performance at ultimate reliability and thus is of great benefit to every researcher and engineer engaged in this diode laser field.

Another novelty and highlight is, for the first time ever in book form, a comprehensive yet concise discussion of diode laser reliability related issues. These are elaborated in four distinct chapters comprising laser degradation physics and modes, optical strength enhancement approaches including mirror passivation/coating and non-absorbing mirror technologies, followed by two highly relevant product-oriented chapters on reliability design engineering concepts and techniques and an elaborate reliability test plan for laser chip and module product qualification. This original and novel approach to link laser design to reliability aspects and requirements provides both, most useful insight into degradation processes such as catastrophic optical mirror damage on a microscopic scale, and a wide selection of effective remedial actions. These accounts, which are of highest significance for lasers operating at the optical stress limit due to extremely high output power densities and most demanding lifetime requirements are very professionally prepared and discussed in an interesting, coherent and skilful manner.        

The diagnostics part, consisting of three very elaborate chapters, is most unique and novel with respect to other diode laser books. It discusses for the first time ever on a very high level and in a competent way studies on material integrity, impurity trapping effects, mirror and cavity temperatures, surface- and interface quality, mirror facet disorder effects, mechanical stress and facet coating instability, and diverse laser temperature effects, dynamic laser degradation effects and mirror temperature maps. Of highest significance to design, performance and reliability are the various correlations established between laser device and material parameters. The most different and sophisticated experiments, carried out by the author at micrometer spatial resolutions and at temperatures as low as 2K, provide highly valuable insights into laser and material quality parameters, and reveal for the first time the origins of high power limitations on an atomic scale due to local heating effects and deep level defects. It is of great benefit, that the experimental techniques such as Raman spectroscopy, various luminescence techniques, thermoreflectance and deep-level transient spectroscopy, pioneered by the author for the specific experiments on lasers, are discussed with great expertise in depth and breadth, and the numerous paper articles published by the author are now represented in this book.

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

I can highly recommend this extremely relevant, well-structured and well-formulated book to all practising researchers in industrial and academic diode laser R&D environments and to post-graduate engineering students interested in the actual problems of designing, manufacturing, testing, characterising and qualifying diode lasers. Due to its completeness and novel approach to combine design, reliability and diagnostics in the same book, it can serve as an ideal reference book as well, and it deserves to be welcomed wordwide by the addressed audience.

Dr. Chung-en Zah, Research Director, Semiconductor Technologies Research, S&T Division, Corning Incorporate, Corning NY, USA 


“Semiconductor Laser Engineering, Reliability and Diagnostics: A Practical Approach to High Power and Single Mode Devices”. By Peter W. Epperlein

Cordinatore Prof. Lorenzo Pavesi, UNIVERSITÀ DEGLI STUDI DI TRENTO, Dipartimento di Fisica   /   Laboratorio di Nanoscienze    

This book represents a well thought description of three fundamental aspects of laser technology: the functioning principles, the reliability and the diagnostics. From this point of view, and, as far as I know, this is a unique example of a book where all these aspects are merged together resulting in a well-balanced presentation. This helps the reader to move with ease between different concepts since they are presented in a coherent manner and with the same terminology, symbols and definitions.

The book reads well. Despite the subtitle indicates that it is a practical approach, the book is also correct from a formal point of view and presents the necessary equations and derivations to understand both the physical mechanisms and the practicalities via a set of useful formulas. In addition, there is the more important aspect of many real-life examples of how a laser is actually manufactured and which the relevant parameters that determine its behaviour are. It impresses the amounts of information that are given in the book: this would be more typical of a thick handbook on semiconductor laser than of an agile book. Dr. Epperlein was able to identify the most important concepts and to present them in a clear though concise way.

I am teaching a course on Optoelectronics and I'm going to advise students to refer to this book, because it has all the necessary concepts and derivations for a systematic understanding of semiconductor lasers with many worked-out examples, which will help the student to grasp the actual problems of designing, manufacturing, testing and using semiconductor lasers. All the various concepts are joined to very useful figures, which, if provided to instructors as files, can be a useful add-on for the use of the book as text for teaching. Concepts are always detailed with numbers to give a feeling of their practical use.

In conclusion, I do find the book suitable for my teaching duties and will refer it to my students.

Prof. Dr. Lorenzo Pavesi, Head of the Department of Physics, Head of the Nanoscience Laboratory, University of Trento, Italy
31 May 2013


“Semiconductor Laser Engineering, Reliability and Diagnostics: A Practical Approach to High Power and Single Mode Devices”. By Peter W. Epperlein

Robert W. Herrick, Ph.D., Senior Component Reliability Engineer, Intel Corp., Santa Clara, California, USA

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

While dozens of books have been written over the past couple of decades on semiconductor laser design, only a handful have been written on semiconductor laser reliability. Prior to the release of this book, perhaps 40% of the material could be obtained elsewhere by combining five books: one on laser design, one on laser reliability, one on reliability calculations, and a

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 diode lasers 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; laser optical 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 mode operation 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 doping 108

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 heterostructures 122

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 mode 133

2.1.4 Narrow-stripe weakly index-guided transverse lateral waveguides 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 mode 141

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; laser length 153 Higher order lateral mode suppression by selective losses 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 kinks 158

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 waveguide lasers 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 layer composition 171 Slope efficiency versus cladding layer composition 172 Slope efficiency versus threshold current density 172 Threshold current versus slow-axis far-field angle 172 Slope efficiency versus slow-axis far-field angle 174 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 angled waveguides 182

2.4.3 Unstable resonator (UR) lasers 183 Introduction 183 Curved-mirror UR lasers 184 UR lasers with continuous lateral index variation 187 Quasi-continuous unstable regrown-lens-train resonator lasers 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 laser characteristics 214

3.1.1 Optical power; threshold; efficiency; and transverse modes 214 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 location 222 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 failure 246

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 process 256

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 of quantum 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 models for 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 distribution acceleration 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 and reliability 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 and module 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 material integrity; impurity trapping effects; and mirror temperatures 361

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 layer 373 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 results 382

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 Raman spectra 396 First laser mirror temperatures by Raman 398

7.4.6 Various dependencies of diode laser mirror temperatures 401 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)GaAs 412

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

8.2 Local mechanical stress in ridge waveguide diode lasers 416

8.2.1 Motivation 416

8.2.2 Measurements – Raman shifts and stress profiles 417

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 instability 424

8.3.1 Motivation 424

8.3.2 Experimental details 424

8.3.3 Silicon recrystallization by internal power exposure 425 Dependence on silicon deposition technique 425 Temperature rises in ion beam- and plasma enhanced chemical 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 maps 433

Introduction 434

9.1 Thermoreflectance microscopy for diode laser diagnostics 435

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-thermoreflectance 445

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-thermoreflectance 451

9.5.1 Motivation 451

9.5.2 Real-time temperature-monitored laser degradation 451 Critical temperature to catastrophic optical mirror damage 451 Development of facet temperature with operation time 453 Temperature associated with dark-spot defects in mirror facets 454

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

9.6 Diode laser cavity temperatures by micro-electroluminescence 456

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-dimensional mapping 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 the active layer 461

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

References 466

Index 469

“With invaluable practical advice, this new reference book is suited to practising researchers in diode laser technologies, and to postgraduate engineering students.”  (The German Branch of the European Optical Society, 1 October 2013)

"This book would be a valuable reference and essential source for researchers and engineers who work on the development of diode laser products. It will also be useful for academics and teachers for educational purposes."  (Optics & Photonics News, 25 October 2013)