Dr. Akasaki conducted persistent research on gallium nitride (GaN) for many years toward the realization of blue LEDs. His efforts culminated in the pioneering realization of GaN-based p-n junctions, which were once believed to be practically impossible. This achievement served as the first firm step toward the eventual commercialization of blue LEDs. To this day, Dr. Akasaki has consistently played a leading role in a series of significant research endeavors. His contributions to them certainly deserve the highest recognition the world over.
Metalorganic vapor phase epitaxial growth of a high quality GaN film using an AlN buffer layer (Amano, H., Sawaki, N., Akasaki, I. and Toyoda, Y.). Applied Physics Letters 48: 353-355, 1986.
Effects of AlN Buffer Layer on Crystallographic Structure and on Electrical and Optical Properties of GaN and Ga1-xAlxN (0<x≤0.4) Films Grown on Sapphire Substrate by MOVPE (Akasaki, I., Amano, H., Koide, Y., Hiramatsu, K. and Sawaki, N.). Journal of Crystal Growth 98: 209-219, 1989.
P-Type Conduction in Mg-Doped GaN Treated with Low-Energy Electron Beam Irradiation(LEEBI) (Amano, H., Kito, M., Hiramatsu, K. and Akasaki, I.). Japanese Journal of Applied Physics 28: L2112-L2114, 1989.
Crystal Growth and Conductivity Control of Group III Nitride Semiconductors and Their Application to Short Wavelength Light Emitters (Akasaki, I. and Amano, H.). Japanese Journal of Applied Physics 36: 5393-5408, 1997.
Breakthroughs in Improving Crystal Quality of GaN and Invention of the p-n Junction Blue-Light-Emitting Diode (Akasaki, I. and Amano, H.). Japanese Journal of Applied Physics 45: 9001-9010, 2006.
Dr. Isamu Akasaki conducted persistently intensive research on gallium nitride (GaN) for many years toward the realization of blue light-emitting diodes (LEDs). His efforts culminated in the pioneering realization of GaN-based p-n junctions, which were believed to be practically impossible. This achievement has stimulated research activities on blue LEDs in Japan and elsewhere, and served as the first firm step toward their eventual commercialization. To this day, Dr. Akasaki has consistently played a leading role in a series of research endeavors. His contributions to the birth and progress of GaN-based blue LEDs deserve the highest recognition the world over.
With their high efficiency and long life, LEDs can be used in a wide range of applications. For this reason, R&D efforts in this area started early on, resulting in the development of red and green LEDs. With the addition of blue LEDs, the three primary colors of light would be complete, raising expectations that LEDs could be used to realize full-color displays and white illumination. It was hoped that the realization of blue laser diodes would allow the dramatic increase in the recording density of optical discs. These high expectations led to several attempts to realize blue LEDs around 1970, with researchers conducting intensive research on the promising material of GaN. However, it was quite difficult to prepare high-quality GaN and control their electrical properties. One could form n-type GaN, but p-type materials indispensable for LEDs remained out of reach. As a result, most researchers gave up on their attempts to develop blue LEDs and withdrew from such attempts by the end of the 1970s.
Dr. Akasaki, however, did not. He resolutely continued his research and went on to find in 1985 that the crystalline quality of GaN can be remarkably enhanced by forming a buffer layer at low temperatures on sapphire substrate before growing GaN crystals. With the cooperation of Dr. Hiroshi Amano, Dr. Akasaki made groundbreaking discoveries in 1989. His work demonstrated that p-type GaN can be formed by doping magnesium atoms into high quality GaN and irradiating them with electron beams. Using this method, he and his group realized the world’s first GaN-based p-n junctions and demonstrated their operation as blue LEDs.
These achievements shed new light on the potential of GaN as a material for blue LEDs and restimulated GaN researches. They induced intense R&D activities to establish the technological basis for the commercialization of blue LEDs. These efforts bore fruit when blue LEDs went on the market in 1993. This device is widely used in displays and lighting. Later, blue laser diodes were commercialized, and played a pivotal role in raising the recording density of optical discs. All through these developments, Dr. Akasaki has played leading roles by his pioneering work for the realization of blue light emitting devices and by his persistent research for the advancement of this field.
For these reasons, the Inamori Foundation is pleased to present the 2009 Kyoto Prize in Advanced Technology to Dr. Isamu Akasaki.
I gained an interest in luminescence when I was assigned to a group working on the fluorescent screens of Braun tubes for televisions at my first job after university. Then, I was involved in research work at Nagoya University on single crystal growth of germanium (Ge) and physical properties of Ge and several other semiconductors. In 1961, I succeeded in growing a Ge single crystal film by what is now known as the “vapor-phase epitaxial growth method.” This achievement led me to a position at the then newly-established Matsushita Research Institute Tokyo, Inc. in 1964, where I began my research on crystal growth and light-emitting devices of III-V compound semiconductors.
In the 1960s, red and yellow-green light-emitting diodes (LEDs) and infrared semiconductor laser had already been realized, but there was no prospect for practical blue light-emitting devices even in the 1970s.
Both of the two essential requirements for creating high-performance blue light-emitting devices, namely, the growth of high-quality single crystals of semiconductors with wide bandgap energy, such as gallium nitride (GaN), and realization of their p-n junction, were extremely difficult to achieve. I set for myself the goal of overcoming these difficulties in some way so that I could develop GaN p-n junction blue light-emitting devices.
As expected, the task of crystal growth was tremendously difficult, and I was forced to go through a continuous process of trial and error. By the late 1970s, many researchers had withdrawn from studies on this “unexplored semiconductor,” but day in and day out I continued my research of GaN crystal growth simple-mindedly, feeling as if I was “exploring the wilderness alone.” Then in 1978, I successfully caught a glimpse of tiny yet high-quality crystals through my microscope, when I sensed the potential of GaN. And again, I decided to go back to the basics, i.e., “crystal growth.” In retrospect, this was a major turning point both in my research and in the R&D history of GaN in general. In 1979, I chose to adopt “metalorganic vapor-phase epitaxy (MOVPE)” which I believed to be the optimal crystal growth method for GaN. The correctness of my own choice has been attested by the fact that even today this method is almost invariably chosen to fabricate GaN-based devices, including blue LEDs.
Since 1981, with the most generous cooperation of graduate students and co-researchers at Nagoya University, I achieved a series of “firsts” in the world, including high-quality GaN using the low-temperature buffer layer technology, p-type conduction by electron beam irradiation of high-quality GaN doped with magnesium, and GaN p-n junction blue LEDs. In my lecture, I would like to speak more about the subsequent developments of my research.