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Wide Bandgap Semiconductors
123
Kiyoshi Takahashi, Akihiko Yoshikawa and Adarsh Sandhu (Eds.)
Wide Bandgap Semiconductors
With 394 Figures and 36 Tables
Fundamental Properties and Modern Photonic and Electronic Devices
Library of Congress Control Number:
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Chiba University
Adarsh Sandhu
Tokyo Institute of Technology
Editors
Kiyoshi Takahashi
ISBN-10 3-540-47234-7 Springer Berlin Heidelberg New YorkISBN-13 978-3-540-47234-6 Springer Berlin Heidelberg New York
SPIN 11688655
2006935324
Akihiko Yoshikawa
Typesetting by SPi using a SpringerCover design: Mr. Kirchner, Heidelberg
Professor EmeritusTokyo Institute of Technology
Chairman (1996 The 162nd Committee on Wide Bandgap
e-mail: [email protected]
DirectorR & D Center
e-mail: [email protected]
Professor
Chairman (2006 )
Japan Society for the Promotion of Science
The 162nd Committee on Wide Bandgap
Japan Society for the Promotion of Sciencee-mail: [email protected]
Associate Professor
Associate Editors
Yoshihiro IshitaniAssociate ProfessorChiba University
Associate Professor
Yoichi Kawakami
Kyoto University
2005)
e-mail: [email protected]
Semiconductor Photonic
Semiconductor Photonic
and Electronic Devices
Nippon EMC Ltd
and Electronic Devices
–
–
Editorial Committee Members
Fumio HasegawaProfessor EmeritusTsukuba UniversityProfessor, Kogakuin University
Hideo KawanishiProfessor, Kogakuin University
Katsumi KishinoProfessor, Sophia University
Hiroyuki MatsunamiProfessor Emeritus, Kyoto UniversityDirector, Innovation Plaza KyotoJapan Science and TechnologyAgency (JST)
Kentaro OnabeProfessor, University of Tokyo
Sadafumi YoshidaProfessor, Saitama University
Preface
The p–n junction was invented in the first half of the twentieth century andthe latter half saw the birth of light emitting diodes: red and yellow/greenin the 1960s and yellow in the 1970s. However, theoretical predictions of theimprobability of synthesizing p-type wide bandgap semiconductors cast a longshadow over hopes for devices emitting in the elusive blue part of the electro-magnetic spectrum, which would complete, with red and green, the quest forthe primary colors making up white light. At a time when many researchersabandoned their efforts on nitrides, Professor Isamu Akasaki of Nagoya Uni-versity at this time remained committed to his belief that “synthesis of highquality GaN crystals would eventually enable p-type doping” and in 1989 hesucceeded in fabricating the world’s first GaN p–n junction light emittingdiode.
Professor Isamu Akasaki kindly accepted our invitation to contribute tothis book and describes his journey ‘from the nitride wilderness’ to the firstexperimental results of blue emission from GaN p–n junctions: Japan’s majorcontribution to the development of wide bandgap semiconductor devices.
The discovery of blue emission from GaN p–n junctions in 1989 was themajor technological turning point during the development of wide bandgapemission devices with wide reaching scientific, industrial and social implica-tions. In Japan, I assembled a group of academics and industrialists to discussthe feasibility of setting up a research committee under the Japanese Societyfor the Promotion of Science (JSPS) to study nitride semiconductor opticaldevices. Together, we submitted a proposal to the JSPS on establishing an‘academic/industrial/government’ committee to assess nitride optical devices.The JSPS accepted our proposal, and a JSPS committee on “Wide Band GapSemiconductors and Optoelectronic Devices”, the 162 Committee, was for-mally set up in 1996. The Committee consists of internationally recognizedleaders who were instrumental in triggering the ‘blue-tsunami’ that led tothe renaissance of blue-light semiconductor research and the birth of a viabletechnology as exemplified by the ubiquitous GaN LEDs.
VIII Preface
In 2001, the Committee’s areas of interest were widened to include widebandgap electronic devices in addition to optical structures. In April 2006,Professor Akihiko Yoshikawa of Chiba University was appointed Chairman ofthe 162 Committee and under his guidance new topics such as nanostructures,biotechnology and high temperature devices, will also be covered.
The invention of the blue LED and laser in the 1990s led to the establish-ment of new industries based on blue technology including solid state trafficsignals, UV nitride lasers in high density DVD recorders, solid state white lightillumination, biotechnology, nano-structures and high temperature devices.
The six chapters of this unique book were written by innovators fromJapanese academia and industry recognized as having laid the foundations ofthe modern wide bandgap semiconductor industry. Apart from the in-depthdescription of recent developments in the growth and applications of nitridesemiconductors, this book also contains chapters on the properties and deviceapplications of SiC, diamond thin films, doping of ZnO, II–IVs and the novelBeZnSeTe /BAlGaAs material systems. Practical issues and problems suchas the effect of defects on device performance are highlighted and potentialsolutions given based on recent research.
I expect that this book will be a valuable source of up to date infor-mation on the physical properties, current trends and future prospects ofwide bandgap semiconductors for professional engineers, graduate students,industrial planners responsible for charting projects and think-tank managersmonitoring developments in the semiconductor electronics industry.
The contents of this book are based on the Japanese language, Wide GapSemiconductors, Optical and Electron Devices, published in March 2006 byMorikita Shuppan Co. Ltd.
I would like to express my sincere thanks to the Industry Club of Japanfor their financial contribution to a part of the cost of preparation of this bookby “Special Fund for the Promotion of Sciences” which was made availableby the Japan Society for the Promotion of Sciences (JSPS).
Finally, I would like to thank the members of the 162 Committee, JSPS,Morikita Shuppan Co. Ltd and Springer Publishing, for their support, timeand energy spent in the production and publication of this book.
Kiyoshi TakahashiChairman of the 162 Committee, JSPS (1996–2005)
Tokyo Institute of TechnologyNippon EMC Ltd
Lifetime of Research on Nitrides –Alone in the Wilderness
I. Akasaki
Blue light emitting devices fabricated using nitride semiconductors are ubiq-uitous. They are used in mobile phones, traffic signals and outdoor screens insoccer stadiums. The situation 30 years ago was a lot different when manygroups withdrew from this subject of research due to unfavorable results. Inspite of the lack of progress in this field at the time, I made a consciousdecision to make research on nitride semiconductors my life work. This is arecollection of my thoughts and memories about my contribution to the bluerenaissance [1–3]. I hope that the mistakes and moments of jubilation willinspire young scientists and engineers to have confidence in your own beliefs,not be swayed by trends and fashions, and move forward with passion andcommitment.
First Meeting with Light Emission and CompoundSemiconductors
In 1952, I graduated from the Faculty of Science of Kyoto University andjoined Kobe Kogyo Corp. (now Fujitsu Ltd). At the time, the company em-ployed many talented researchers and was committed to a wide range of re-search activities. Two years after my arrival, the company was one of the firstto begin manufacturing cathode ray tubes for televisions; I was put in chargeof the fluorescent screens. Polycrystalline, powder Zn(Cd)S-based phosphorswere applied to the interior of the CRT face plate and electron irradiationenabled production of images. Now, Zn(Cd)S is a group II–VI compoundsemiconductor and this was my first ‘meeting’ with these materials and lu-minescence. Looking back, this work had a great effect on my research careerimplicitly and explicitly, publicly and privately, in every possible way.
In the early 1950s, industrial researchers were pre-occupied with the impli-cations of the invention of the transistor and Kobe Kogyo already had a teamworking on the development of transistors using single crystal Ge. The term‘single crystal’ resonated with me because of the problems I was having with
X I. Akasaki
the poor reproducibility of experimental data due to polycrystalline Zn(Cd)Spowder for the CRT screens. I seriously considered, and dreamt, about thepossibility of using single crystal Zn(Cd)S and transparent Zn(Cd)S thin filmsfor the CRT screens. Perhaps this unconscious interest in single crystal semi-conductors was part of the reason I worked on single crystal GaAs, GaPand GaN, which emit light, during my days at Matsushita Research InstituteTokyo, Inc. (MRIT).
In 1959, I accepted an invitation to move to the Department of Electronicsat Nagoya University where I worked with Professor Tetsuya Arizumi onsetting up a series of technologies ranging from production of Ge ingots byreduction of germanium oxide and subsequent purification by zone refining,growth of single crystals, impurity doping, and device fabrication. At thetime, p–n junctions were produced by diffusing arsenic (or antimony) intoslices of p-type Ge. However, I was anxious about this method: the n-regionin p–n junctions formed by ‘diffusion’ was compensated with p-type impuritieswhich were introduced beforehand, and the impurity distribution is limitedto the complementary error function. In order to overcome these drawbacks,I thought a new method about which was later known as ‘epitaxial growth’ ofthin film semiconductors by which single crystalline Ge films could be grownthrough gas phase reactions of Ge compounds on Ge substrates. In collabo-ration with Professor Nishinaga (a prospective graduate student at that timeand current president of Toyohashi University of Technology), we studied va-por phase epitaxial growth (VPE) of Ge from its very inception. I think thatthis research laid the foundations for my work at MRIT on epitaxial com-pound semiconductors including metalorganic vapor phase epitaxial growth(MOVPE) of nitride semiconductors. In fact my work on Ge epitaxy was thereason for an invitation by MRIT to join their new institute in 1964.
The Nitride Challenge
At Matsushita, I was put in charge of a laboratory with freedom to decide myresearch activities. My basic policy for semiconductor research was “make ourown crystals, characterize their physical properties, use the results to optimizegrowth conditions, produce extremely high quality crystals and develop noveldevice applications”. At the time, I first focused on the growth of so-called‘magic crystal’, namely GaAs and related III–V compounds such as GaP,GaAsP, GaInP and their development for red and green/yellow light emittingdiodes. In spite of the fact that I managed to produce the best results forsuch materials at the time, for a variety of reasons, these semiconductors werenot used for fabrication of commercial devices. However, I was determined todevelop blue light emitting devices using p–n junctions; something that noone had yet succeeded in producing.
Realization of blue light emitting devices requires growth of high qual-ity single crystals of semiconductors with bandgaps (Eg) larger than 2.6 eV
Lifetime of Research on Nitrides – Alone in the Wilderness XI
and control of their electrical conductivity, in particular realization of p-typematerial. At the time, however, theoretical studies indicated the improbabilityof achieving p-type ZnSe and other such wide bandgap semiconductors dueto self compensation; almost all the major groups were pessimistic about re-alization of ZnSe and in particular GaN p–n junctions. The only example ofsuccess was SiC p–n junctions used to produce green/yellow emitting devices.However, I had absolutely no interest in this material for photonic deviceapplications because of its indirect bandstructure did not enable the possi-bility of achieving high emission efficiency and hence laser oscillation wouldbe impossible. Soon after my move to Matsushita, my belief in the potentialof nitrides led me to start research on the VPE growth of AlN (1966) [4] inparallel to the GaAs-based work. I confirmed blue emission from AlN usingCL and PL and was enjoying working with light emitting materials, but ELwas not possible due to the excessively large bandgap.
Thus, in 1973 I decided to focus first on GaN growth.In fact, in 1969, Maruska et al. [5] had reported on the growth of single
crystals of GaN by hydride vapor phase epitaxy (HVPE) and used opticalabsorption to determine its bandstructure to be direct with Eg of ∼3.39 eV.Then in 1971, Pankove et al. fabricated MIS-type blue LEDs [6]. These reportstriggered a sudden increase in research on blue light emitting devices [Fig. 1,period (A)]. However, the surfaces of GaN crystals were very rough withcracks and pits, and p-type GaN was impossible to produce. Thus manygroups retired from GaN research and some moved on to other materialssuch as ZnSe and activities on nitrides declined [Fig. 1, period (B)]. From myexperience of VPE growth of high quality GaAs [7], I was confident that dras-tic improvements in the crystal quality of GaN would eventually enable p-typeconduction of this material as well. My view was, “It is too early to discussself-compensation in poor quality GaN. High quality GaN crystals (residualdonor density of at least less than 1015 cm−3) must first be produced beforediscussing such physical properties.”
Then in 1973, I decided to make “realization of blue light emitting devicesby GaN p–n junctions”, an idea abandoned by many, my life’s work.
A slight digression, but at the time, apart from groups working on SiC,almost all researchers were studying ZnSe which has a direct bandgap of∼2.7 eV and shows bright CL and PL emission. In addition, its lattice constantis similar to GaAs thus enabling epitaxial growth on GaAs substrates. Thusmany researchers were reasonable in thinking of ZnSe as being the first choiceas a material for blue or green light emitting devices. (Later, in 1986, very fewpeople showed interest in GaN even after we reported on the successful growthof high quality GaN crystals.) However, apart from ZnSe being ‘softer’ thanGaN, I was also anxious about the crystallinity and stability of ZnSe becauseof its low growth temperature. On the other hand, the melting point and vaporpressure of GaN are both much higher than ZnSe making its crystal growthextremely difficult. In addition, the Eg of GaN is very large compared withZnSe, which makes it much more difficult to produce p-type GaN compared
XII I. Akasaki
Fig. 1. Number of Publications (INSPEC) and activities related to nitrides between1965 and 2000. All events are marked in the years, when they were first achieved.Most of important results were achieved by MOVPE using LT-buffer layer after1986. It is clear that the start of the steep increase of numbers of publicationsand accomplishments is due to the key inventions (high quality GaN, conductivitycontrol and p–n junction blue LED etc.) in the late 1980s. Green: Crystal Growth,Blue: Devices, Red: Conductivity Control and Physics
with ZnSe crystals. However, I was not discouraged by the problems with GaNbecause I still believed in the potential of GaN and once the problems wereresolved, then compared with ZnSe, nitrides would enable production of morerobust and shorter wavelength p–n junction light emitting devices.
Lifetime of Research on Nitrides – Alone in the Wilderness XIII
Choice of MOVPE as the Preferred Growth Method
Until 1973, GaN was mostly grown by HVPE and no one used molecular beamepitaxy (MBE). However, I decided to use MBE for the first time. Using Gaand NH3 as sources, I was able to produce single crystal GaN, albeit materialwith non-uniformities. I sent a proposal for a project entitled, ‘Developmentof blue light emitting devices by ion implantation into single crystal GaN’ tothe Ministry of International Trade and Industry (MITI) at the time and in1975, was awarded a three-year research grant to conduct the project [8].
Following many difficulties, and with the assistance of my team of re-searchers at MRIT, we were able to produce blue GaN LEDs with muchbetter emission characteristics than ever reported, and succeeded in achievingthe aims of the project. Approximately 10,000 GaN blue light emitting testdevices with the newly developed as-grown cathode electrodes were manufac-tured (an example is shown in Fig. 2). But due to poor surface uniformity andlow yield of MIS structures, the devices were not sold commercially. My goalwas p–n junction devices, so I was not discouraged by the lack of success ofthese MIS LEDs. Two years later, we reported our results at an internationalconference [9] (where we were the only group to report on GaN related work)but without much of a reaction since most researchers had lost interest inGaN work.
Fig. 2. Fountain display using tricolor LEDs, which was later in 1981 demonstratedin Chicago by Matsushita Electric Industrial Co. Ltd
XIV I. Akasaki
However, as a result of my increasing experience with handling GaNcrystals, fluorescence microscopy showed the existence of high quality micro-crystals in parts of larger crystals containing cracks and pits. Also, we foundthat clusters of needle-like crystals (‘GaN-fungus!’) left inside the growthreactors exhibited highly efficient light emission. From these experiences, Ireconfirmed the great potential of GaN and believed that p-type GaN couldindeed be produced if a whole wafer could be made of the same quality as theGaN microcrystals left in the growth reactor.
I then decided to go back to basics and reconfirm the fundamentals ofcrystal growth: I had experience of growing at least ten kinds of semiconduc-tors and intuitively I knew that crystal quality depended greatly on growthconditions and hence the choice of growth method would be the critical factorin determining the future of the research.
Epitaxial GaN can be grown by MBE, HVPE and MOVPE. MBE wasprone to nitrogen desorption and also the growth rate was slow at the time.In HVPE, the growth rate was too fast and crystal quality was affected byreversible reactions. So I thought that this method was not suitable for pro-ducing high quality crystals.
On the other hand, the MOVPE method, which at the time was hardlyused for GaN growth, uses thermal dissociation reactions at a singletemperature and has negligible reversible reactions. Also, the growth ratewas intermediate between the other two methods thus enabling growth ofnitrides on substrates with a large lattice mismatch. Thus in 1979, I decidedto adopt MOVPE as the most suitable method for the growth of GaN. An-other advantage of this method was that alloy composition and impuritydoping could be readily controlled by varying the source flow rate. Lookingback, this decision had a tremendous effect on the development of nitridesemiconductors (Fig. 1, caption).
The next problem was the choice of substrate. I experimented with growthon Si, GaAs and sapphire substrates. Eventually, in 1979 I decided on usingsapphire because it was stable at temperatures above 1,000oC as well as beingable to withstand NH3 during growth. This choice, at the time, was alsoappropriate and afterwards led to the first demonstration of p–n junctionblue LEDs.
Two Important Breakthroughs
In 1981, I returned to my old nest at Nagoya University. One of the mostimportant research themes of my group was ‘research and development of bluelight emitting devices using GaN based p–n junctions’. Prospective graduatestudents who showed interest in this theme included Hiroshi Amano (nowprofessor at Meijo University) and Yasuo Koide (now group leader (OpticalSensor Group) of National Institute for Materials Science)). With the supportof my colleague, associate professor Nobuhiko Sawaki (now professor and dean
Lifetime of Research on Nitrides – Alone in the Wilderness XV
of Graduate School of Engineering, Nagoya University) and Koide and Amano,I set up a clean room and MOVPE growth facilities. In spite of our efforts,however, MOVPE growth did not yield favorable results.
I thought that the main reason was because of the extremely large interfa-cial energy between GaN and sapphire due to the large mismatches betweenthese materials. Then I had an idea: the insertion of a soft, ‘low temperature(LT) buffer layer’ to relax the strain. For the buffer layers, I thought aboutusing AlN, GaN, ZnO and SiC because these materials had similar physicalproperties to those of GaN and sapphire. In a discussion with Amano, I saidthat the buffer layers should be less than 50 nm and deposited at less than500oC. Amano, in spite of the poor results up until that time, worked in-tensely on the use of MOVPE for growth of GaN. Quite accidentally, whenthe growth reactor was not functioning properly, he deposited a thin AlN layerat low temperature (according to my suggestion) followed by the growth ofGaN on top. He showed me the sample he had just grown: the GaN surfacewas flat and optically transparent [Fig. 3 (right)] [10]. I can still rememberthe excitement at seeing the reality of the dreams of my Matsushita days:mirror-like, crack and pit free, transparent GaN crystals.
The residual donor density of the GaN crystals grown with LT-buffer layerwas also drastically reduced [10,11] but in spite of repeated efforts on acceptor-doping, it was not possible to produce conducting p-type materials using Znas a dopant. In 1987, when Amano was carrying out CL measurements onhigh quality Zn-doped GaN crystals grown with the LT-buffer layer, he saidthat “the emission intensity continues to increase the longer we irradiate theZn-doped GaN sample with the electron beam during the CL measurements”.I thought that this was an important observation, which might be related tothe p-type conduction, and asked for more detailed measurements. The re-sults did not show p-type conduction, but the discovery was that: Zn-related
Fig. 3. Optical images of GaN grown on sapphire by MOVPE without (a) and with(b) LT-AlN buffer layer. The latter is transparent and crack and pit free
XVI I. Akasaki
blue luminescence from Zn-doped high quality GaN crystals grown with theLT-buffer layers increased as a result of electron beam irradiation. I calledthis phenomenon the LEEBI effect. This discovery was reported in 1988 [12].Meanwhile at the beginning of 1988, we noticed that Mg would have smallerionization energy than Zn and started doping experiments using Mg insteadof Zn. Even though at the time the delivery time was several months, we usedCp2Mg and MCP2Mg, as Mg sources and grew Mg-doped GaN layers on sap-phire covered with the LT-buffer layers [13]; these experiments were mainlycarried out by a prospective graduate student, Masahiro Kito (now manager,Intellectual Property Center of Semiconductor Company, Matsushita Elec-tric Industrial Co., Ltd). The Mg-doped GaN samples were irradiated withelectron beams in the same way as the Zn-doped samples. We found greatlyincreased Mg-related blue emission from such Mg-doped GaN samples as wellas the samples being low resistivity p-type GaN from Hall Effect measure-ments: the discovery of p-type conduction in nitride semiconductors. Soonafterwards, we fabricated a GaN p–n junction blue/UV LED (Fig. 4) for thefirst time, and reported its encouraging I–V characteristics [14].
In 1989, we also succeeded in controlling the conductivity of n-type ni-trides using high quality nitride crystals grown with the LT-buffer layer incombination with SiH4 doping [15]. This control of the conductivity of n-typenitrides is very important as well as the realization of p-type conduction. In1990, we demonstrated room temperature stimulated emission in the UV re-gion for the first time, which is indispensable for laser operation, from thehigh quality GaN grown with the LT-buffer layers [16].
Fig. 4. The world’s first GaN p–n junction blue LED on a sapphire substratedeveloped in 1989. Only one LED is emitting light. The I–V characteristics of aGaN p–n junction LED and MIS-LED
Lifetime of Research on Nitrides – Alone in the Wilderness XVII
These breakthroughs (achieved in period (C) in Fig. 1) inspired nitrideresearchers around the world to greater efforts and eventually led to the com-mercialization of high performance blue LEDs, violet laser diodes and relateddevices as shown in period (D) in Fig. 1.
Conclusion
Thirty years ago, the fabrication GaN p–n junction blue light emitting deviceswas a dream which was finally realized ten years ago. This technology will haveprofound implications in the future. Of course, this technology is the result ofcontributions from not only myself, but many people including my colleaguesat Matsushita Research Institute Tokyo, collaborators and talented studentsat Nagoya University and Meijo University and industrialists whose favorableevaluation of our findings led to commercial devices.
I am truly grateful to the many friends and research collaborators whoI had the good fortune to work with over the last 40 years.
Finally, to young researchers I would like to say, “mistakes accompany newchallenges but are overtures to discovery.”
References
1. I. Akasaki: Mater. Res. Soc. Symp. Proc. 639, (2001) G8.1.12. I. Akasaki: Oyo Buturi 71 (2002) 814 (in Japanese)3. I. Akasaki: Oyo Buturi 73 (2004) 1060 (in Japanese)4. I. Akasaki and M. Hashimoto: Solid State Commun. 5 (1967) 8515. M.P. Maruska and J.J. Tietjen: Appl. Phys. Lett. 15 (1969) 3276. J.I. Pankove, E.A. Miller, and J.E. Berkeyheiser: RCA Rev. 32 (1971) 3837. I. Akasaki and T. Hara: Proc. 9th Int. Conf. Phys. Semicond. IX (1968) 7878. For example I. Akasaki and I. Hayashi: Kogyo Gijutsu 17 (1976) 48 (in Japanese)9. Y. Ohki, Y. Toyoda, H. Kobayashi, and I. Akasaki: Inst. Conf. Ser. 63 (1981)
47910. H. Amano, N. Sawaki, I. Akasaki, and Y. Toyoda: Appl. Phys. Lett. 48 (1986)
35311. I. Akasaki, H. Amano, Y. Koide, K. Hiramatsu, and N. Sawaki: J. Cryst. Growth
98 (1989) 20912. H. Amano, I. Akasaki, T. Kozawa, K. Hiramatsu, N. Sawaki, K. Ikeda, and Y.
Ishii: J. Lumin. 40 & 41 (1988) 12113. H. Amano, M. Kito, K. Hiramatsu, and I. Akasaki: J. Electrochem. Soc. 137
(1990) 163914. H. Amano, M. Kito, K. Hiramatsu, and I. Akasaki: Jpn J. Appl. Phys. 28 (1989)
L211215. H. Amano and I. Akasaki: Ext. Abstr. Mater. Res. Soc. EA-21 (1990) P16516. H. Amano, T. Asahi, and I. Akasaki: Jpn J. Appl. Phys. 29 (1990) L205
Contents
PrefaceK. Takahashi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII
Lifetime of Research on Nitrides –Alone in the WildernessI. Akasaki . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IX
1 Development and Applications of Wide BandgapSemiconductorsA. Yoshikawa, H. Matsunami and Y. Nanishi . . . . . . . . . . . . . . . . . . . . . . 11.1 Optical Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Wide Bandgap Semiconductors Indispensable for ShortWavelength Optical Devices . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.2 Control of the Physical Properties of III–V Nitridesand II–VI Semiconductors . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1.3 Other Characteristics and Trends of Wide BandgapSemiconductor Optical Devices . . . . . . . . . . . . . . . . . . . . . . . 10
1.2 Electronic Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111.2.1 Silicon Carbide Electronic Devices . . . . . . . . . . . . . . . . . . . . 111.2.2 Nitride Compound Semiconductor Electron Devices . . . . . 16
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2 Fundamental Properties of Wide Bandgap SemiconductorsS. Yoshida, T. Ito, A. Hiraki, H. Saito, S. Fujita, Y. Ishitani, S. Sakai,T. Miyajima, Y. Yamada, Y. Kawakami, I. Suemune, K. Hiramatsu,H. Kawanishi, H. Amano, H. Okumura and T. Mizutani . . . . . . . . . . . . 252.1 Crystals and Band Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.1.1 IV–IV Group Semiconductors . . . . . . . . . . . . . . . . . . . . . . . . 252.1.2 II–VI Semiconductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312.1.3 III–V Nitride Semiconductors . . . . . . . . . . . . . . . . . . . . . . . . 362.1.4 Heterostructures and Band Structure . . . . . . . . . . . . . . . . . 412.1.5 Lattice Defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
XX Contents
2.2 Optical, Mechanical, and Thermal Properties of Wide BandgapSemiconductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522.2.1 Optical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522.2.2 Quantum Structure of Wide Bandgap Semiconductors . . 632.2.3 Lattice Constants of Semiconductors . . . . . . . . . . . . . . . . . . 672.2.4 Mechanical and Thermal Properties of Semiconductors . . 70
2.3 Electrical Properties of Wide Bandgap Semiconductors . . . . . . . . . 772.3.1 Doping Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 772.3.2 Mobility of Electrons and Holes . . . . . . . . . . . . . . . . . . . . . . 782.3.3 Electrical Properties of SiC . . . . . . . . . . . . . . . . . . . . . . . . . . 802.3.4 Electrical Properties of GaN . . . . . . . . . . . . . . . . . . . . . . . . . 82
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
3 Photonic DevicesY. Kawakami, S. Kamiyama, G. Hatakoshi, T. Mukai, Y. Narukawa,I. Nomura, K. Kishino, H. Hirayama, M. Kawasaki, A. Ohtomo,H. Okushi, Y. Taniyasu, M. Kasu, T. Makimoto, A. Hirano,K. Kohmoto, H. Kanie, N. Shibata, T. Nakamura, K. Tadatomo,M. Kuramoto, T. Yanamoto, H. Amano and K. Akimoto . . . . . . . . . . . . 973.1 Physical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
3.1.1 Fundamental Properties of Optical Devices . . . . . . . . . . . . 973.1.2 Optical Gain and Laser Action . . . . . . . . . . . . . . . . . . . . . . . 105
3.2 Visible LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1113.2.1 Visible AlGaInP LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1113.2.2 Visible GaN LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1143.2.3 BeZnSeTe-Based Green LEDs . . . . . . . . . . . . . . . . . . . . . . . . 120
3.3 Ultraviolet Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1243.3.1 Issues Related to the Development of High Efficiency
and Short Wavelength Ultraviolet LEDs . . . . . . . . . . . . . . . 1243.3.2 ZnO LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1313.3.3 Diamond Light Emitting Devices . . . . . . . . . . . . . . . . . . . . . 1403.3.4 AlN LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1463.3.5 Ultra Violet Photodetectors . . . . . . . . . . . . . . . . . . . . . . . . . 152
3.4 White Light Emitting Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1583.4.1 White LEDs for Illumination . . . . . . . . . . . . . . . . . . . . . . . . 1583.4.2 Development Trends of Phosphors . . . . . . . . . . . . . . . . . . . . 1603.4.3 Improvements of the Color Rendering of GaN-Based
White LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1673.4.4 High Efficiency and High-Power LEDs . . . . . . . . . . . . . . . . 1703.4.5 ZnSe-Based White LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1753.4.6 Applications and Prospects of White Light
Emitting LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1803.5 Laser Diodes (LDs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
3.5.1 Blue/Violet Laser Diodes for Next Generation DVDApplications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
Contents XXI
3.5.2 Long Wavelength GaN-Based Laser Diodes . . . . . . . . . . . . 1983.5.3 Advances in UV Laser Diodes . . . . . . . . . . . . . . . . . . . . . . . . 2063.5.4 ZnSe Laser Diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
4 Electronic DevicesH. Miyamoto, M. Arai, H. Kawarada, N. Fujimori, S. Yoshida,T. Shinohe, A. Hiraki, H. Hiraki, H. Koinuma and M. Katayama . . . . 2314.1 High Frequency Power Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
4.1.1 Nitride Semiconductor High FrequencyPower Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
4.1.2 SiC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2394.1.3 Diamond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
4.2 High Breakdown Voltage, High CurrentDensity Power Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2494.2.1 GaN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2494.2.2 SiC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
4.3 New Functional Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2634.3.1 Electron Emitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2634.3.2 Transparent Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
5 Novel Nano-Heterostructure Materials and Related DevicesH. Kumano, I. Suemune, K. Kishino, S. Fujita, A. Sandhu, N. Suzukiand K. Ohkawa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2815.1 Nanostructure Devices and Materials . . . . . . . . . . . . . . . . . . . . . . . . 281
5.1.1 Single Photon Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2815.1.2 GaN Nanocolumn Light Emitting Devices . . . . . . . . . . . . . 2875.1.3 Wide Bandgap Semiconductor Nanostructures
and Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2965.2 Novel AlGaN/GaN Heterostructure Devices . . . . . . . . . . . . . . . . . . . 298
5.2.1 GaN-Based High Temperature OperatingHall Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
5.2.2 GaN-Based Intersubband Transition Optical Switches . . . 3035.2.3 Nitride Photocatalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
6 Crystal GrowthN. Ohtani, T. Nakamura, H. Sumiya, F. Hasegawa, S. Sarayama,T. Taniguchi, K. Watanabe, S. Fujiwara, Y. Kashiwaba, I. Niikura,T. Kimoto, T. Egawa, H. Okushi, K. Onabe, K. Tadatomo,K. Hiramatsu, A. Yoshikawa, H. Kawanishi, K. Akimoto, T. Yaoand T. Hanada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3296.1 Bulk Crystal Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
6.1.1 SiC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3296.1.2 Diamond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
XXII Contents
6.1.3 GaN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3426.1.4 BN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3486.1.5 ZnSe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3526.1.6 Crystal Growth of Bulk ZnO Single Crystal . . . . . . . . . . . . 356
6.2 Epitaxial Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3626.2.1 Epitaxial Growth of SiC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3626.2.2 GaN/Si Epitaxy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3706.2.3 Diamond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3796.2.4 Epitaxial Growth of GaN. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3836.2.5 InGaN and InGaN/GaN Heterostructures . . . . . . . . . . . . . 3936.2.6 AlGaN, AlN, and AlGaN/GaN Heterostructures . . . . . . . 4006.2.7 InN and Related Semiconductors . . . . . . . . . . . . . . . . . . . . . 4076.2.8 Lattice-Matched Quaternary BAlGaN Alloys . . . . . . . . . . 4156.2.9 Epitaxial Growth of ZnSe and Related Semiconductors . . 4176.2.10 ZnO and Related Semiconductors . . . . . . . . . . . . . . . . . . . . 427
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
List of Contributors
Akasaki, IsamuProfessor EmeritusNagoya UniversityMeijo University
Akimoto, KatsuhiroUniversity of Tsukuba
Amano, HiroshiMeijo University
Arai, ManabuNew Japan Radio Co., Ltd
Egawa, TakashiNagoya Institute of Technology
Fujimori, NaoharuNational Institute of AdvancedIndustrial Science and Technology(AIST)
Fujita, ShizuoKyoto University
Fujiwara, ShinsukeSumitomo Electric Industries, Ltd
Hanada, TakashiTohoku University
Hasegawa, FumioProfessor EmeritusUniversity of TsukubaKogakuin University
Hatakoshi, Gen-IchiToshiba Corporation
Hiraki, AkioProfessor EmeritusOsaka UniversityKochi University of Technology
Hiraki, HirohisaKochi University of Technology
Hiramatsu, KazumasaMie University
Hirano, AkiraOsaka Gas Co., Ltd
Hirayama, HidekiRIKEN
Ishitani, YoshihiroChiba University
Ito, ToshimichiOsaka University
Kamiyama, SatoshiMeijo University
XXIV List of Contributors
Kanie, HisashiTokyo University of Science
Kashiwaba, YasubeIwate University
Katayama, MasaoTokyo Institute of Technology
Kawakami, YoichiKyoto University
Kawanishi, HideoKogakuin University
Kawarada, HiroshiWaseda University
Kawasaki, MasashiTohoku University
Kimoto, TsunenobuKyoto University
Kishino, KatsumiSophia University
Kohmoto, KohtaroTeknologue Co., Ltd
Koinuma, HideomiProfessor EmeritusTokyo Institute of TechnologyJapan Science and TechnologyAgency (JST)
Kumano, HidekazuHokkaido University
Kuramoto, MasaruSony Corporation
Matsunami, HiroyukiProfessor EmeritusKyoto UniversityDirector, Innovation Plaza KyotoJapan Science and TechnologyAgency (JST)
Miyajima, TakaoSony Corporation
Miyamoto, HironobuSumitomo Electric Industries, Ltd
Mizutani, TakashiNagoya University
Mukai, TakashiNichia Corporation
Nakamura, TakaoSumitomo Electric Industries, Ltd
Nanishi, YasushiRitsumeikan University
Narukawa, YukioNichia Corporation
Niikura, IkuoIwate University
Nomura, IchirouSophia University
Ohkawa, KazuhiroTokyo University of Science
Ohtani, NoboruNippon Steel Corporation
Ohtomo, AkiraTohoku University
Okumura, HajimeNational Institute of AdvancedIndustrial Science and Technology(AIST)
Okushi, HideyoNational Institute of AdvancedIndustrial Science and Technology(AIST)
List of Contributors XXV
Onabe, KentaroUniversity of Tokyo
Saito, HiroshiOkayama University of Science
Sakai, ShiroUniversity of Tokushima
Sandhu, AdarshTokyo Institute of Technology
Sarayama, SeijiRicoh Co., Ltd
Shibata, NaokiToyoda Gosei Co., Ltd
Shinohe, TakashiToshiba Corporation
Suemune, IkuoHokkaido University
Sumiya, HitoshiSumitomo Electric Industries, Ltd
Suzuki, NobuoToshiba Corporation
Tadatomo, KazuyukiYamaguchi University
Takahashi, KiyoshiProfessor EmeritusTokyo Institute of TechnologyNippon EMC Ltd
Taniguchi, TakashiNational Institute for MaterialsScience (NIMS)
Taniyasu, YoshitakaNTT Corporation
Watanabe, KenjiNational Institute for MaterialsScience (NIMS)
Yamada, YoichiYamaguchi University
Yanamoto, TomoyaNichia Corporation
Yao, TakafumiTohoku University
Yoshida, SadafumiSaitama University
Yoshida, SeikohFurukawa Electric Co., Ltd
Yoshikawa, AkihikoChiba University
