Impact of GaN transition layers in the growth of GaN epitaxial layer on silicon

A method for growing GaN epitaxial layer on Si(111) substrate is investigated. Due to the large lattice mismatch between GaN and Al N, GaN grown directly above an Al N buffer layer on the Si substrate turns out to be of poor quality. In this study, a GaN transition layer is grown additionally on the Al N buffer before the GaN epitaxial growth. By changing the growth conditions of the GaN transition layer, we can control the growth and merging of islands and control the transfer time from 3D to 2D growth mode. With this method, the crystalline quality of the GaN epitaxial layer can be improved and the crack density is reduced. Here, we have investigated the impact of a transition layer on the crystalline quality and stress evolution of a GaN epitaxial layer with methods of X-ray diffraction, optical microscopy and in situ reflectivity trace. With the increasing thickness of transition layer, the crack decreases and the crystalline quality is improved. But when the transition layer exceeds a critical thickness, the crystalline quality of the epilayer becomes lower and the crack density increases.