Nondestructive evaluation of misfit dislocation densities in ZnSe∕GaAs heterostructures by x-ray diffuse scattering

Estimating the low densities of misfit dislocations in epitaxial layers in the early stages of relaxation is difficult, requiring a very sensitive method. The characteristic patterns of diffuse x-ray scattering are therefore utilized to quantify the linear density of misfit dislocations. This is demonstrated for ZnSe∕GaAs(001) heterostructures with ZnSe layer thickness slightly above the critical thickness. The densities that resulted from calculated patterns of x-ray scattering perpendicular to the diffraction vector are found to be in good agreement with the results of cathodoluminescence and transmission electron microscopy. Moreover, the diffuse x-ray scattering is used to quantitatively study the thermally induced increase in the linear densities of misfit dislocations. Samples are annealed at various temperatures for increasing periods successively and are analyzed between the annealing steps by high-resolution x-ray diffraction. The density of dislocations is found to saturate for longer annealing periods. The saturation value and the rate of increase of the dislocation density depend both on the annealing temperature and on the crystallographic direction.