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 grown GaN epilayer by molecular-beam epitaxy is investigated. It is found that decreasing the N/Ga flux ratio during the buffer layer growth yields excess Ga in the buffer layer. GaN epilayers grown on the buffer layer with excess Ga showed increased electron Hall mobility and reduced threading dislocation density. The tilt and twist disorders of the epilayer were also significantly reduced. The compressive stress in the epilayers at room temperature increased as the N/Ga flux ratio during the buffer layer growth was reduced. The improved properties of the epilayers are explained by the hypothesis that excess Ga in the buffer layer facilitates stress relaxation at the epilayer growth temperature.