Key inventions in the history of nitride-based blue LED and LD

It was quite difficult to grow high quality single crystals of nitrides and impossible to control their electric conduction. These problems prevented the development of nitride-based devices for many years. In 1986, a dramatic improvement in the crystalline quality of GaN was achieved by use of low-temperature-deposited (LT) buffer layer technology in metalorganic vapor phase epitaxy. In 1989, the high quality GaN enabled us to produce p-type conduction in nitrides and to control the conductivity of n-type nitrides. These achievements led to the invention of the world's first GaN p–n junction blue/UV LED in 1989. Room temperature UV stimulated emission, which is indispensable for laser operation, was also achieved in 1990 by use of high quality GaN films grown with the LT-buffer layers. These breakthroughs inspired nitride researchers around the world to greater efforts, and eventually led to the commercialization of high-performance blue LEDs and long-life violet LDs as well as the development of nitride-based devices such as high-speed transistors. Furthermore, unique properties such as a large piezoelectric effect were also clarified due to the marked improvements in crystal quality of nitrides. In this paper, key inventions during the development of nitride-based blue LED and LD are reviewed and a recent advance in UV devices is also described.