ABSTRACT
In the search of light sources covering the whole visible spectrum, GaN, which has a large direct band gap, is a sure one to study. Bright luminescence in the bluelgreen range can be seen, and devices in MIS (metal-insulator-semiconductor) structure are obtained in 1971 by Pankove. After more than a decade, breakthroughs emerge in a series of events. In 1983, Yoshida puts down an AlN buffer layer on sapphire before the GaN growth using MBE (molecular beam epitaxy) technique, and gets good results on the properties of GaN films. In 1986, Akasaki uses MOCVD (metal-organic chemical vapor deposition) to grow the AlN buffer layer on sapphire at low temperature, and the GaN film quality improves considerably. Another big leap comes in 1989 when Akasaki successfully activates the Mg dopants using LEEBI (low energy electron beam irradiation) to break up Mg-H bond. Nakamura follows with annealing in an Hfree environment to activate the Mg acceptors.
