Grazing incidence small-angle x-ray scattering study of buried and free-standing SiGe islands in a SiGe/Si superlattice

We present a method to interpret reciprocal-space maps recorded in grazing-incidence small-angle x-ray scattering geometry to obtain the shape and the lateral correlation properties of buried islands. From the maps, which have been recorded for various penetration depths, the autocorrelation function is calculated, from which the island parameters are obtained by comparison with simulations based on the distorted-wave Born approximation. As a demonstration of the sensitivity of the method, measurements on self-organized SiGe islands in a Si/SiGe multilayer have been performed. It was possible to detect different shapes of the islands at the sample surface and those embedded in the multilayer. For a comparison with atomic force microscopy, we employ the same method to analyze images of the islands at the top surface.