SEMICONDUCTOR LASERS. Second Edition. The Institute of Optics, University of Rochester Rochester, New York. and. Niloy K. Dutta

Transcription

1 SEMICONDUCTOR LASERS

2 SEMICONDUCTOR LASERS Second Edition Govind P. Agrawal The Institute of Optics, University of Rochester Rochester, New York and Niloy K. Dutta AT&T Bell Laboratories Murray Hill, New Jersey.., ~ KLUWER ACADEMIC PUBLISHERS BOSTONIDORDRECHTILONDON

3 Distributors for North, Central and South America: Kluwer Academic Publishers 101 Philip Drive Assinippi Park Norwell, Massachusetts USA Telephone (781) Fax (781) Distributors for all other countries: Kluwer Academic Publishers Group Distribution Centre Post Office Box AH Dordrecht, THE NETHERLANDS Telephone Fax Electronic Services < Library of Congress Cataloging-in-Publication Agrawal, G.P. (Govind P.), Semiconductor lasers / Govind P. Agrawal and Niloy K. Dutta.--2nd ed. p. cm. First ed. published 1986 under title: Long-wavelength semiconductor lasers. Includes bibliographical references and index. ISBN-13: e-isbn-13: : / Semiconductor lasers. I. Dutta, N.K. (Niloy K.), II. Agrawal, G.P. (Govind P.), Long-wavelength semiconductor lasers. III. Title. TA1700.A '61--dc eip Copyright 1993 by AT&T Third printing 2001 by Kluwer Academic Publishers Softcover reprint of the hardcover 2nd edition 2001 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, mechanical, photo-copying, recording, or otherwise, without the prior written permission of the publisher, Kluwer Academic Publishers, 101 Philip Drive, Assinippi Park, Norwell, Massachusetts Printed on acid-free paper. This printing is a digital duplication of the original edition.

4 CONTENTS Preface to the First Edition/xiii Preface to the Second Edition/xv 1. Introduction/1 1.1 Historical Perspective/1 1.2 Semiconductor Materials/5 1.3 Operating Principles/ p-n Junction/ Dielectric Waveguide/II Recombination Mechanisms/ Laser Threshold/ Optical Fiber Communications/ Overview /19 Problems / 21 References / Basic Concepts/ Introduction/ Maxwell's Equations/ Threshold Condition and Longitudinal Modes/ Gain and Stimulated Emission/ Waveguide Modes/ Effective Index Approximation/ Transverse Modes/ Lateral Modes/ Emission Characteristics/ Light-Current Characteristics/ Spatial-Mode Characteristics/ Spectral Characteristics/ Dynamic Characteristics/70 Problems/70 References/71 v

5 vi CONTENTS 3. Recombination Mechanisms in Semiconductors/ Introduction/ Radiative Recombination/ Absorption and Emission Rates for Discrete Levels/ Absorption and Emission Rates in Semiconductors/ Absorption Coefficient and Optical Gain/ Nonradiative Recombination/ Band-to-Band Auger Processes/ Phonon-Assisted AugeJ;.. Processes/ Defect and Surface Recombination/ Experimental Results/ Threshold Current Density / Carrier Leakage over the Heterojunctions/ Temperature Dependence of Threshold Current/ Carrier-Lifetime Measurements/ Optical-Gain Measurements/ External Differential Quantum Efficiency/ Discussion/139 Problems/142 References/ Epitaxy and Material Parameters of InGaAsP / Introduction/ Liquid-Phase Epitaxy/ LP E Apparatus/ Growth Methods/ LPE of InGaAsP/ Vapor-Phase Epitaxy / Metal-Organic Vapor-Phase Epitaxy/ Molecular-Beam Epitaxy/ Lattice-Mismatch Effects/ Material Parameters/ Band-Structure Parameters/ Mobility/ Refractive Index/17l 4.8 Strained-Layer Epitaxy /174 Problems/176 References/ Laser Structures and Their Performance/ Introduction/ Broad-Area Lasers/181

6 CONTENTS vii 5.3 Gain-Guided Lasers/ Weakly Index-Guided Lasers/ Strongly Index-Guided Lasers/ Leakage Current/ Laser Arrays/ Surface-Normal Emitting Lasers/223 Problems/226 References/ Rate Equations and Operating Characteristics/ Introduction/ Rate Equations/ Steady-State Characteristics/ Light-Current Curve/ Longitudinal-Mode Spectrum/ Transient Response/ Dynamic Longitudinal-Mode Spectrum/ Turn-On Delay/ Relaxation Oscillations/ Noise Characteristics/ Langevin Formulation/ Intensity Noise/ Phase Noise and Line Width/ Modulation Response/ Small-Signal Analysis/ Intensity Modulation/ Frequency Chirping/ Large-Signal Modulation/ Ultrashort Pulse Generation/ External Optical Feedback/ Modified Rate Equations/ Steady-State Behavior / Dynamic Behavior/ Noise Characteristics/306 Problems/309 References/ Distributed-Feedback Semiconductor Lasers/ Introduction/ DFB Laser Structures/ Theory /323

7 viii CONTENTS Coupled- Wave Equations/ Longitudinal Modes and Threshold Gain/ Coupling Coefficient/ Threshold Behavior/ Light-Current Characteristics/ Performance/ CW Operation/ Modulation Performance/ Phase-Shifted DFB Lasers/ Multiquantum-Well DFB Lasers/ Gain-Coupled DFB Lasers/ DBR Lasers/ Design Issues/ Theory/ Emission Characteristics/ Tunable Semiconductor Lasers/ Transmission Experiments/371 Problems/376 References/ Coupled-Cavity Semiconductor Lasers/ Introduction/ Coupled-Cavity Schemes/ Theory / Coupling Constant / Longitudinal Modes and Threshold Gain/ Side-Mode Suppression/ Modulation Response/ Operating Characteristics/ Longitudinal-Mode Control/ Optimum Biasing for Direct Modulation/ Frequency Chirp/ Transmission Experiments/ External-Cavity Semiconductor Lasers/ Diverse Applications/416 Problems/422 References/ Quantum-Well Semiconductor Lasers/ Energy Levels/ Density of States/430

8 CONTENTS ix 9.3 Experimental Observation of Confined States/ Radiative Recombination/ Auger Recombination/ Single Quantum-Well and Multiquantum-Well Lasers/ MQW Laser Results/ Modulation and Noise Characteristics/ Strained Quantum-Well Lasers/462 Problems/468 References/ Surface-Emitting Lasers/ Introduction/ Mirror Refiectivity/ GaAs-AIGaAs and InGaAs-GaAs Surface-Emitting Lasers/ InGaAsP-InP Surface-Emitting Lasers/ Laser Arrays/484 Problems/485 References/ Optical Amplifiers/ Introduction/ General Concepts/ Gain Spectrum and Bandwidth/ Gain Saturation/ Amplifier Noise/ Amplifier Applications/ Semiconductor Laser Amplifiers/ Impact of Facet Reflectivity/ Amplifier Designs/ Amplifier Characteristics/ Multichannel Amplification/50B Pulse Amplification/51O System Applications/ Multiquantum-Well Amplifiers/ Fiber Amplifiers/ Energy Levels/ Fiber Amplifier Performance/524 Problems/526 References/527

9 x CONTENTS 12. Photonic and Optoelectronic Integrated Circuits/ Introduction/ Photonic Integrated Circuits/ Arrays/ Integrated Laser Detector/ Integrated Laser Modulator/ Integrated Laser Amplifier/ Heterodyne Receiver/ Optoelectronic Integrated Circuits (OEICs)/ Receiver OEICs/ Transmitter OEICs/ Regenerator OEICs/ Logic OEICs/543 References/ Infrared and Visible Semiconductor Lasers/ Lead-Salt Lasers/ Materials and Physical Properties/ Band Structure/ Optical Gain/ Auger Recombination/ Laser Diode Fabrication/ Laser Properties/ Tuning Characteristics/ Other Material Systems/ Infrared Semiconductor Lasers/ Visible Semiconductor Lasers/574 Problems/578 References/ Degradation and Reliability / Introduction/ Defect Formation in the Active Region/ Experimental Techniques/ Electroluminescence/ Photoluminescence/ Cathodoluminescence/ Dark Defects under Accelerated Aging/ Catastrophic Degradation/ Degradation of Current-Confining Junctions/595

10 CONTENTS xi 14.5 Reliability Assurance/ Stress Aging/ Activation Energy/ DFB Laser Reliability /603 Problems/605 References/605 Index/607

11 PREFACE TO THE FIRST EDITION Since its invention in 1962, the semiconductor laser has come a long way. Advances in material purity and epitaxial growth techniques have led to a variety of semiconductor lasers covering a wide wavelength range of ~ m The. development during the 1970s of GaAs semiconductor lasers, emitting in the near-infrared region of ~ m resulted, in their use for the first generation of optical fiber communication systems. However, to take advantage oflow losses in silica fibers occurring around 1.3 and 1.55 ~ m the, emphasis soon shifted toward long-wavelength semiconductor lasers. The material system of choice in this wavelength range has been the quaternary alloy InGaAsP. During the last five years or so, the intense development effort devoted to InGaAsP lasers has resulted in a technology mature enough that lightwave transmission systems using InGaAsP lasers are currently being deployed throughout the world. This book is intended to provide a comprehensive account of long-wavelength semiconductor lasers. Particular attention is paid to InGaAsP lasers, although we also consider semiconductor lasers operating at longer wavelengths. The objective is to provide an up-to-date understanding of semiconductor lasers while incorporating recent research results that are not yet available in the book form. Although InGaAsP lasers are often used as an example, the basic concepts discussed in this text apply to all semiconductor lasers, irrespective of their wavelengths. The book is aimed at researchers already engaged in or wishing to enter the field of semiconductor lasers. It should serve as a useful reference for engineers who are interested in optical fiber communications and want to know about the semiconductor-laser sources employed therein. The book can also be useful for a graduate-level course on semiconductor lasers as part of a program in optical communications. We have attempted to make the book self-contained and to provide sufficient details of the mathematical derivations. Furthermore, each chapter refers to a large number of published papers that can be consulted for further study. The book is organized as follows. The first three chapters introduce the basic concepts and provide the mathematical derivations useful for xiii

12 xiv PREFACE TO THE FIRST EDITION understanding the operation of semiconductor lasers. Chapters 4 and 5 describe epitaxial techniques and various device structures employed to fabricate semiconductor lasers. The operating characteristics of these lasers are considered in Chapter 6, including static, dynamic, spectral, noise, and modulation aspects. The next two chapters are devoted to single-frequency semiconductor lasers employing the distributed-feedback and coupled-cavity schemes, while Chapter 9 considers quantum-well semiconductor lasers. The degradation mechanisms and reliability issues of semiconductor lasers are discussed in Chapter 10. Finally, Chapter 11 considers lead-salt semiconductor lasers emitting at relatively longer wavelengths in the far-infrared region 3-34/lm. We wish to thank the members of the semiconductor laser development department and other colleagues at AT&T Bell Laboratories for numerous discussions and for providing a stimulating working environment. We are thankful to D. P. Wilt and C. H. Henry for their comments on several chapters. The support of the AT&T Bell Laboratories management for this project is gratefully acknowledged. We particularly thank R. W. Dixon, J. E. Geusic, and P. J. Anthony for their encouragement. G. P. Agrawal N. K. Dutta

13 PREFACE TO THE SECOND EDITION The field of semiconductor lasers has advanced considerably since the publication of the first edition in Among the recent advances, to name a few topics, are surface-emitting semiconductor lasers, high-power laser arrays, visible semiconductor lasers, and strained layer quantum-well lasers. The second edition is intended to bring this book up to date so that it remains a source of comprehensive coverage on semiconductor lasers. Whereas the first edition focused mainly on long-wavelength semiconductor lasers (mostly InGaAsP lasers), the scope of this edition has been widened to include all kinds of semiconductor lasers, as reflected by the change in the title of the book. Since the first edition has occasionally been used as a textbook in some graduate-level courses, we have added selective problems at the end of each chapter to help teachers and students. It is our hope that the second edition can serve as a textbook for graduate courses dealing with semiconductor lasers. Selective chapters can also be useful for other courses related to lasers, optoelectronics, and optical communications. The list of topics that could have been included in the second edition was quite large. Size limitations forced us to make a selection. It was felt that surface-emitting semiconductor lasers, semiconductor laser amplifiers, and optoelectronic integration needed enough coverage that a new chapter was justified for each of them. The main change consists of adding three new chapters (Chapters to, 11, and 12) and several new sections to the existing chapters. Major changes are made in Chapters 6, 7, and 9 while other chapters are updated to bring the discussion up to date. Specifically, a section on mode-locked semiconductor lasers is added to Chapter 6. The advances in the field of distributed feedback semiconductor lasers are covered by adding a section on tunable semiconductor lasers and three sections on phase-shifted, quantum-well, and gain-coupled distributed feedback lasers. Chapter 9 has a new section on strained-layer quantum-well lasers, a topic that has attracted considerable attention in recent years. Visible semiconductor lasers are included in Chapter 13. We feel that these additions have improved the text enough that it should serve the need of the scientific community during the 1990s. We would welcome suggestions and comments from the readers. G. P. Agrawal N.K.Dutta xv