SEMICONDUCTOR SCIENCE IN JAPAN
JUN-ICHI NISHIZAWA
Semiconductor power electronics is opening a new prospect towards sustainable society with least energy dissipation and least pollution. Highly efficient semiconductor power electron devices such as static induction thyristros (SIThy) will enable high voltage direct current (HVDC) power transmission. Comparing three major energy sources i.e., steam power, nuclear power and water power generations, there are serious problems of the increase of CO2 concentration in the air and nuclear disposals for the former two. On the other hand, the water power generation is almost free from air pollution and harmful disposals. The water powers which will be generated at long and large rivers in the world can be transported by HVDC to any place at long distances over 10,000 km, which is nearly equivalent to a quarter of the peripherals of the glove. High efficiency SIThy converters also enable practical electric cars which are possible to replace the present cars so that they will contribute to much reduction of air pollution and fossil energy consumption. SITthys have DC-AC conversion efficiency exceeding 99%. They have very high power and high speed capability for both turn-on and off actions; for example, the 2500V 150A to 4000V 400A class single gate SIThys were developed. As for the switching speed, double gate SIThy showed the most excellent characteristics such as turning-on and off time faster than 0.4 µs. Light triggered and light quenched SIThys allow to control high voltage without electrical connections so that power handling will become safe.On the other hand, semiconductor science aims to contribute to achieve a society which utilizes tremendous capacity of information. In particular, compound semiconductor materials researches, as well as device researches, are important for further progress of optical communication and electronics. Based on the fundamental study of deviation from stoichiometry, growth of nearly perfect crystals of GaAs was realized. They were applied to the production of highly efficient LEDs. Recent advances of the crystal growth with atomic accuracy like molecular layer epitaxy will enable the semiconductor devices which will operate at terahertz frequency.