X-RAY-DIFFRACTION PEAK PROFILES FROM HETEROEPITAXIAL STRUCTURES WITH MISFIT DISLOCATIONS

X-ray diffraction peak profiles of relaxed heteroepitaxial layers with randomly distributed misfit dislocations are simulated and compared w ith the experimental data for two systems, LPE-grown SiGe/Si and MBE-g rown AlSb/GaAs heterostructures. Different types of correlations in th e spatial distribution of misfit dislocations are considered. For rela tively small dislocation densities in the SiGe/Si system, the observed peaks are broader than the calculated ones for uncorrelated distribut ions of 60 degrees dislocations. This broadening is explained as a res ult of a non-uniform tilt of the layer due to variations in the densit ies of dislocations with different Burgers vectors. In the AlSb/GaAs s ystem possessing a high density of misfit dislocations, the peak of th e relaxed AlSb buffer layer is found to be essentially narrower than e xpected from the model of uncorrelated dislocations. This effect can b e explained by the short-range spatial corrrelations in the positions of the dislocations.