X-ray diffraction peak profiles from heteroepitaxial structures with misfit dislocations

Abstract

X-ray diffraction peak profiles of relaxed heteroepitaxial layers with randomly distributed misfit dislocations are simulated and compared with the experimental data for two systems, LPE-grown SiGe/Si and MBE-grown AlSb/GaAs heterostructures. Different types of correlations in the spatial distribution of misfit dislocations are considered. For relatively small dislocation densities in the SiGe/Si system, the observed peaks are broader than the calculated ones for uncorrelated distributions of 60° dislocations. This broadening is explained as a result of a non-uniform tilt of the layer due to variations in the densities of dislocations with different Burgers vectors. In the AlSb/GaAs system possessing a high density of misfit dislocations, the peak of the relaxed AlSb buffer layer is found to be essentially narrower than expected from the model of uncorrelated dislocations. This effect can be explained by the short-range spatial correlations in the positions of the dislocations.