S. Nakamura, G. Fasol . The Blue Laser Diode Springer-Verlag Berlin Heidelberg GmbH Shuji Nakamura Gerhard Fasol The Blue Laser Diode GaN Based Light Emitters and Lasers With 246 Figures and 49 Tables Springer Shuji Nakamura Gerhard Fasol, Ph. D. Nichia Chemical Industries Ltd. Eurotechnology Japan Ltd. 491, Oka, Kaminaka Parkwest Building 11th Floor Anan, Tokushima-ken 774 6-12-1 Nishi-Shinjuku Japan Shinjuku-ku, Tokyo 160 e-mail: [email protected] Japan e-mail: [email protected] Libary of Congress, Cataloging· in-Publication Data applied for Die Deutsche Bibliothek - CIP-Einheitsaufnahme Nakamura, Shuji: The blue laser diode: GaN based light emitters and lasers / Shuji Nakamura; Gerhard Fasol. - Berlin; Heidelberg; New York; Barcelona; Budapest; Hong Kong; London; Milan; Paris; Santa Clara; Singapore; Tokyo: Springer, 1997. NE: Fasol, Gerhard ISBN 978-3-662-03464-4 ISBN 978-3-662-03462-0 (eBook) DOI 10.1007/978-3-662-03462-0 This work is subject to copyright. 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Typesetting: Camera-ready copies from the authors Cover design: design & production GmbH, Heidelberg SPIN 10543597 57/3144 - 543210 - Printed on acid-free paper Preface Shuji Nakamura's development of commercial light emitters from Gallium Nitride and related materials has recently propelled these materials into the mainstream of interest. It is very rare that a breakthrough of such proportion can be converted so quickly into successful commercial products. One factor for this success is Shuji Nakamura's hard work, another factor is Nichia's enlightened founder, Chairman and joint owner, Nobuo Ogawa without whom Nakamura probably could not have done this work, other factors are Professor Pankove's and Professor Akasaki's pioneering work. The amazing speed of GaN breakthroughs caused an information gap. There is much less information available on GaN then on silicon or GaAs, and most current semiconductor text books do not even mention Gallium Nitride. One of the aims of the present book is to close this information gap, another important aim is to provide a report on the development of Gal­ lium Nitride based light emitters and lasers and their properties. Both aims are rapidly moving targets: recent results near the end of the book even report, that InGaN lasers might become the first commercial lasers using self-assembled quantum dots. The present book also documents an amazing success story of great his­ torical importance. At the time when Nichia's Chairman Nobuo Ogawa gave Shuji Nakamura several million dollars budget to 'gamble' on GaN research, Nakamura was an unknown 36 old engineer, without a Ph.D., without a single publication, and no commercially successful product developments. Maybe this story has some more general relevance at a time when we can observe that scientific research is being rapidly reengineered everywhere, so that it survives or, even better, leads a rapidly and profoundly changing world. Silicon circuits have replaced vacuum tubes in radios and computers. Gallium-Nitrides (together with other compound semiconductors) may well soon replace light bulbs and fluorescent tubes in a similar way. And they have other nice applications, too. Anan and Tokyo, January 1997 Shuji Nakamura, Gerhard Fasol Foreword by Shuji Nakamura This book is written about III-V nitride materials such as CaN, InCaN, AICaN, AICalnN, their crystal growth, blue/green/yellow /white light emit­ ting diodes (LEDs), purplish-blue laser diodes (LDs) and their applications. Why should III-V nitride materials be described in this book? You probably have some questions about the motivations. First, considering environmental issues, III-V nitride materials will become very important because they will reduce energy consumption by replacing conventional light sources such as light bulbs or fluorescent lamps. Using III-V nitride materials we can already fabricate highly efficient long-lifetime solid state light sources such as LEDs and LDs instead of conventional vacuum tube light bulbs which were devel­ oped by Thomas Alva Edison in 1879 1 . Edison's electrical light bulbs replaced gas lighting soon after their invention. Using these solid state light sources energy consumption would be reduced to 1/10 in comparison with that of conventional light bulbs. Also, the lifetime of III-V nitride based LEDs is more than 106 hours, i.e. almost forever. On the other hand, the lifetime of conventional light bulbs is less than 103 hours. Using LEDs as light sources, we no longer need replacements for burned lamps after installing. Thus we could reduce the number of nuclear power plants worldwide by saving energy using III-V nitride based solid state light sources instead of conventional vac­ uum tube light sources. Also, III-V nitride materials are not toxic to humans, in contrast to conventional II-VI or III-V compound semiconductor materi­ als. The safety of materials is very important for many private and public applications to be carried out under safe and healthy conditions. Thus, from the environmental viewpoint, people should have some knowledge about these issues and consider the use ofIII-V nitride based LEDs for many applications to reduce energy consumption and in order to protect our environment. The III-V nitride based materials system is a mysterious material from the viewpoint of physics because the performance of blue/green CaN based LEDs is superior to conventional red CaAIAs and AlInCaP LEDs with respect to output power and reliability, in spite of the large number of crystal defects (to the order of 1010 cm2 ). Also, the lifetime of InCaN based multi-quantum-well structure LDs is now more than 30 hours under RT CW operation which is almost comparable with that of ZnSe based LDs (100 hours). However, 1 US-Patent No. 223,898 VIII Foreword by Shuji Nakamura the dislocation density of ZnSe based crystals is below 103 /cm2 -107 times lower! It seems that dislocations in III-V nitride materials do not work as nonradiative recombination centers. I started III-V nitride based LED research in 1989 after leaving a study of GaAs bulk crystal growth and AIGaAs liquid phase epitaxial (LPE) growth at my company. At that time, nobody could imagine the present popularity of III-V nitride semiconductors and device performance such as high-brightness blue/green LEDs and violet LDs using III-V nitride materials. During the period 1989 - 1992, I attended several domestic conferences to study the GaN research of other groups. It was surprising that the number of participants was so small (only a few people in addition to the speaker) at the nitride sessions. On the other hand, the number of participants for ZnSe sessions was huge - more than 500 people - at Japanese domestic conferences. This trend became even greater after the success of the first laser oscillations using ZnSe based materiels in 1991 by the 3M group. Nobody could have imagined at that time that the popularity of GaN and ZnSe could be completely reversed within a few years. This is an amazing development of physics research. I joined Nichia Chemical Industries Ltd. in 1979 at a time when it was still a very small company (the number of employees was about 200). Nichia was a chemical company and not a semiconductor company. The company's speciality was the production of phosphors for color cathode ray (CRT) tubes and for fluorescent lamps (the worldwide market share is about 30% now). I was assigned to the R&D department on joining the company, and I started semiconductor research such as GaP, GaAs bulk crystal growth and GaAIAs LPE growth for the red and infrared LED markets with no special knowledge of compound semiconductors, with no assistant staff, and with no collabora­ tion with other universities and companies, nor with large funds since Nichia was a small fragile company. I spent a lot of effort to develop these prod­ ucts. However, the sales of these products were not good, despite successes in production, due to the severe competition from other Japanese giant semi­ conductor companies. Thus, I spent ten years on III-V compound bulk crystal growth and LPE growth without any business success. My company was not happy with the outcome of my research because the resulting business was poor. Dissatisfied with the lack of commercial succes of my research, and I changed my research subject to blue LEDs using III-V nitride materials be­ cause there was no competition in the area of III-V nitride based blue LEDs and LDs from any big companies in 1989. All big companies and universities were doing ZnSe research for blue emitters at that time. That was my most important reason for selecting II 1-V nitride materials for blue emitters, since my previous research had always been in competition with big companies. What I have managed to achieve shows that anybody with relatively little special experience in a field, no big money and no collaborations with other universities and companies, can achieve considerable research success alone when he tries a new research area without being obsessed by conventional Foreword by Shuji Nakamura IX ideas and knowledge.