Depth distribution of strain in GaN/AlN/SiC heterostructures by DUV micro-Raman spectroscopy

We measured the depth distribution of strain in GaN/AlN/SiC heterostructures by using deep ultraviolet (DUV) micro-Raman and photoluminescence spectroscopies with bevel shaped specimens. Raman signal of AlN were detectable for the layers thicker than 15 nm. AlN and GaN layers had compressive strain in the whole region and the strain relaxation along the growth direction was observed. In this study, the variation of the Raman shift was well explained by a strain relaxation model that the misfit dislocations are distributed not only at the interface, but also throughout the film. The relaxation rate related to the generation rate of misfit dislocations was different for the AlN and GaN layers grown by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD). (C) 2007 WILEY-VCH Verlag GmbH & Co. KG&A, Weinheim