Managing Director of the Board (R&D Center, Optoelectronics Sales Div.), TOYODA GOSEI CO., LTD.
Nitride semiconductor LEDs
Blue LEDs were not considered to be developed during the 20th Century.
Prof. Akasaki aggressively spent his life for developing GaN which is a material suitable for Blue LEDs.
As a result, the following all fundamental technologies for Blue LEDs (used for White converted LEDs) were established first in the world.
1) Crystallization of high quality GaN
2) n-type GaN
3) p-type GaN
These LEDs are used for large size full screen displays, backlights of cell phones and notebook PCs, and recently penetrating into LCD TVs and light sources of general lighting. Its market size is huge and unpredictable.
Toyoda Gosei started the R and D of Blue LEDs in 1986 under Prof. Akasaki's supervision and commercialized Blue LEDs.
In this report, the history of Blue LED development is reviewed, and its technologies progress and applications including the future technologies are introduced.
Masao Ikeda
R&D Director and Chief Distinguished Engineer, Advanced Materials Laboratories, Sony Corporation
Nitride semiconductor LDs
Stimulated by the fact that the GaN-based laser diode (LD) was successfully realized using breakthroughs brought by Prof. Akasaki et al., we changed our direction of developing short-wavelength LD based on II-VI materials for use in next-generation optical disk systems, toward development based on nitride materials. Thanks to the rigid nature of GaN-based materials, such as stable threading dislocations in the active layers which are never multiplied by current injection, and a high critical optical power density for catastrophic optical damage of laser facets, the development of reliable and high-power LDs progressed quite satisfactorily, resulting in the successful commercialization in Blu-ray Disc, PS3, and so on. Recently in collaboration with Tohoku University, we started to investigate pico-second super high-power lasers as an attempt to pursue the potential performance of GaN-based LD and expand applications. The superior potential of GaN-based materials has already been demonstrated by 12 W peak-power under gain-switching operation, which was one order of magnitude higher than the power reported for other material systems. In this talk therefore, I would like to present our recent results of pico-second super high-power LDs based on GaN-based materials.
Abstracts
Fumio Hasegawa
Professor Emeritus, University of Tsukuba
Nitride semiconductor high-speed and power devices
--- Present status and future prospect of AlGaN/GaN HFETs ---
Compound semiconductor electron devices have to always compete with Si devices in cost as well as in performance, differently from light emitting devices. Even if output power and efficiency (performance) is 1.5 times better than those of Si devices, compound semiconductor electron devices can not be sold in twice price.
There are two applications for nitride electron devices; microwave devices and power switching devices. The former is already used for power amplifiers of meteorological radars and satellite communications as replacement of klystrons and traveling wave tubes. They are expensive, lower reliable than semiconductor devices and need a high voltage power supply, therefore, expensive nitride devices can be used. The biggest potential market of the power switching device is those for hybrid and electric vehicles. Normally off operation is inevitable for the switching device for vehicles. Several structures have been proposed and demonstrated, but the performance is not enough yet. A structure with an essential normally off mechanism should be developed even if it needs a complicated structure with a difficult fabrication process.
Yasuhiko Arakawa
Professor, Institute of Industrial Science, The University of Tokyo
Nitride semiconductor nanostructures
The nitride semiconductor science established by the pioneering achievement of Dr. Isamu Akasaki has emerged in the last decade as innovative technologies for blue light-emitting diodes, lasers and FETs which are indispensable in future IT societies. On the other hand, the concept of quantum dots proposed in 1982 has brought up unique features of artificial atoms, leading to a wide variety of experimental investigations into semiconductor physics and device applications. In particular, a remarkable progress of InAs-based quantum dot technology has resulted in commercialization of the quantum dot lasers in the quite near future. In this presentation, we overview recent advances in GaN-based nanostructures with emphasis on physics, growth, and device applications of quantum dots and nanowires. Outlook and issues of research fields of GaN-based nanostructures are also addressed.
Abstracts
Akira Usui
Executive Officer, R&D Division, Furukawa Co., Ltd.
Reduction of defects in nitride semiconductors
The first report on semiconductor GaN crystal growth was published in 1969, where the growth was carried out by HVPE (hydride vapor phase epitaxy) method on a sapphire substrate. However, the crystallinity was insufficient because the large island growth was dominant on the substrate. Important breakthrough was in a low-temperature buffer layer technique proposed by Dr. Akasaki et al, which becomes a standard process to grow nitrides materials on foreign substrates. However, in order to improve device performances, further reduction of dislocation density was needed. The lateral overgrowth method was proposed to satisfy with such requirement. In this technique, the generation of dislocations in the overgrown layer on the mask was suppressed and threading dislocations were largely reduced by the bending effect due to facet planes appeared on the side walls of selective-area growth clusters. In this talk, the reduction of defects in nitride semiconductors using above techniques will be discussed by focusing on the preparation of GaN crystal by HVPE.
Katsumi Kishino
Professor, Faculty of Science and Engineering, Sophia University
Nitride Semiconductor Nanocolumns
Nanodevices have attracted considerable attention from researchers. Nitride semiconductor nanocolumns are one-dimensional nanocrystals of typically 20-300nm diameter and 2m height. Using their dislocation-free property and high light extraction efficiency, the fabrication of high-efficiency nano-emitters producing green to red emission is highly expected. Initially, GaInN-based nanocolumns were grown through the self-assembling technique, but this introduced fluctuations in the size and position of nanocolumns, bringing about multicolor emissions. Thus we have developed a selective-area-growth technique to control the nanocolumn size and position, and a uniform array of nanocolumns was successfully fabricated. The photoluminescence emission from the InGaN quantum well was then evaluated, and we observed that the emission color changed monotonically from blue, green to red. This phenomenon indicates the possibility of realizing full-color nanodevices, such as three-primary-color nanoemitters, nanopixel devices and so forth, using GaInN-based nanocolumns. A two-dimensional periodic arrangement of nanocolumns generates strong light confinement at a specific wavelength, by which the first stimulated emission from GaInN-based nanocolumns was observed.
Abstracts
Yoichi Kawakami
Professor, Graduate School of Engineering, Kyoto University
Optical processes in nonpolar and semipolar nitride semiconductors
Twenty years has passed since the first achievement of the pn-conductivity-control in GaN. Thereafter, the development of light emitting diodes (LEDs) and laser diodes (LDs) has been made day by day, reaching to the realization of highly efficient light emitting devices based on InGaN, covering from near ultraviolet to blue spectral region. However, the problem still exists, where the sufficient efficiency cannot be obtained in the wavelength longer than blue-green range if In compositions are further increased. This mechanism is now understood as a result of huge internal electric fields induced by piezo-electric polarization in In-rich InGaN quantum wells grown on polar GaN (c-plane in hexagonal phase). Accordingly, this problem has led to the intensive research, where the fabrication and basic study have been performed in the InGaN/GaN hetero-structures grown on nonpolar substrates (tilted 90° with respect to c-plane), and on semipolar ones (tilted in the range of 0° to 90° with respect to c-plane). I will introduce the key developments and the future prospects in nonpolar and semipolar nitride materials and devices.
Hiroshi Amano
Professor, Faculty of Science and Engineering, Meijo University
Development of group III nitride semiconductors for light emitting, photodetector and solar cells covering infrared to UV region
High performance UV to green LEDs, white LED composed of blue LED and yellow phosphors, and violet laser diode have been commercialized using GaN-based AlGaInN semiconductors. UV and green laser diodes have also been developed by this material system. Potential of this material should not be limited from UV to green region. It is theoretically possible to fabricate infrared devices using InN and VUV devices using AlN. The highest efficiency solar cell is also possible by using tandem structure of this material system. However, due to the lack of suitable growth technique for In-rich GaInN and Al-rich AlGaN, we are unable to fabricate such novel devices. Recently, we developed new growth technology for In-rich GaInN and Al-rich AlGaN, by which we can grow high quality GaInN and AlGaN. In this presentation, new growth technology for group III nitride semiconductors having the whole compositional range will be shown.
Abstracts
Yasushi Nanishi
Professor, College of Science and Engineering, Ritsumeikan University
Professor, Department of Materials Science and Engineering, Seoul National University
Advancement of Indium Nitride Based Semiconductors
Bandgap energy of Indium Nitride (InN) has believed to be 1.9 eV for more than 30 years. Seven years have passed since narrow bandgap energy of around 0.7 eV was reported and this new value is well recognized these days after extensive discussions on this subject. Not only band gap energy, many physical parameters like effective mass, mobility and peak velocity are all revised. Owing to these new findings, new potential applications of nitride semiconductors and alloys like very high efficiency solar cells, wide spectrum range light emitters and sensors from deep UV to IR, high frequency electronic devices up to Terahertz operation are opened up. Several serious issues like reproducible and high quality crystal growth, high density residual carries, p-type doping and high density surface accumulated carriers should be resolved, however, before InN and related alloys are successfully applied to actual devices. Review on these recent advancements of InN and related alloys will be presented in this talk.
Marcos Pinto
17862728
Electronica del estado solido
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