High resolution synchrotron X-ray studies of phase separation phenomena and the scaling law for the threading dislocation densities reduction in high quality AlGaN heterostructure

Abstract

High resolution X-ray coplanar (symmetric X-ray diffraction (SXRD) and asymmetric X-ray diffraction (ASXRD)) and non-coplanar diffraction (grazing incidence diffraction (GID)) have been used to investigate the quality of AlGaN epilayers with 20% Al content, grown on sapphire using SiNx interlayers. The measurement of reciprocal space maps (RSM) with higher orders of reflections of SXRD and ASXRD which is readily performed at the synchrotron with high resolution and intensity reveals the presence of several diffraction peaks originating from the occurrence of local differences in the lattice constants. Two distinguishable AlGaN phases having different crystalline parameters were clearly recognized from X-ray data and the corresponding densities of screw dislocations have been determined measured as function of the overgrowth thickness varying from 0.5μm to 3.5μm. The variation of the screw and edge type dislocation densities with the overgrowth thickness has been found to follow the scaling law h−n where h is the thickness of the buffer layer.