Residual strain in GaN epilayers grown on sapphire and (6H)SiC substrates

A high-resolution multiple-crystal reflection diffractometer was used to determine the residual strain in GaN epilayers grown on different substrates. Our results show that the GaN epilayers with thickness of about 1 mu m are not fully relaxed. The strain situation in a GaN epilayer grown on SiC substrate is totally different from that in GaN layer on sapphire, which are the main reason for the scatter in the recent data on the optical properties of group III nitrides. (C) 1996 American Institute of Physics.