History of Blue LED Consisted of Nitride Semiconductors

The electric energy used for illumination is said to be a quarter of total electric energy consumed on the earth. It is extremely effective to raise the luminous efficiency in order to realize the sustainable society. Furthermore, in the case of night illumination by using electric batteries charged from solar cells in the developing countries where electricity is not supplied, the high efficient emission is indispensable. The history of electrical illumination begins with an incandescent electric lamp. By inventing a fluorescent lamp, the luminous intensity has been improved from 15 Im/W to 95 lm/W, Presently., white light-emitting-diodes (LEDs) consisted of nitride semiconductors have been widely used because their efficiency is at least twice higher than that of a fluorescent lamp. The key device for realizing a white LED is a blue one. In this paper, the history of blue LED consisted of nitride semiconductors is reviewed.