GaN thin films by growth on Ga-rich GaN buffer layers

The influence of the composition of the low-temperature GaN buffer layer on the structural, electrical, and optical properties of the subsequently gro wn GaN epilayer by molecular-beam epitaxy is investigated. It is found that decreasing the N/Ga flux ratio during the buffer layer growth yields exces s Ga in the buffer layer. GaN epilayers grown on the buffer layer with exce ss Ga showed increased electron Hall mobility and reduced threading disloca tion density. The tilt and twist disorders of the epilayer were also signif icantly reduced. The compressive stress in the epilayers at room temperatur e increased as the N/Ga flux ratio during the buffer layer growth was reduc ed. The improved properties of the epilayers are explained by the hypothesi s that excess Ga in the buffer layer facilitates stress relaxation at the e pilayer growth temperature. (C) 2000 American Institute of Physics. [S0021- 8979(00)00223-1].