ABSTRACT
GaN-on-sapphire substrate technology is very mature and is the mainstream in the light-emitting diode (LED) market, but it is unsuitable for power applications due to the poor thermal conductivity of sapphire. A common problem in the growth of GaN on Si is melt-back etching. A GaN epilayer is usually grown at a high temperature of 1000 C using metal-organic chemical vapor deposition (MOCVD). AlN is the most universal nucleation layer that supports high-quality GaN on a Si substrate. Although crack-free GaN films with low wafer bow have been obtained on Si substrates by using stress engineering methods, there still are various issues to overcome, such as the high buffer leakage and the current collapse. Compensational doping, thick buffer layers, the AlGaN/GaN/AlGaN double heterostucture, and Si substrate removal are effective in increasing the breakdown voltage. Increasing of the thickness of the buffer layer will enlarge the distance from the electrode to the Si substrate, which thus can raise the breakdown voltage.
