Strain and composition in SiGe nanoscale islands studied by x-ray scattering

High-resolution x-ray diffraction has been performed on strained SiGe nanoscale islands grown coherently on Si(001). Reciprocal space maps show a widely extended butterfly-shaped island reflection and strong diffuse scattering around the substrate reflection. From such intensity maps the Ge content and its distribution inside the islands are evaluated. This is done by simulation of diffuse scattering for a variety of island models. The island shape is known from atomic force and scanning electron microscopy. The only free parameter was the Ge distribution, here approximated by a vertical concentration profile. With an abrupt increase of Ge content at about one third of the island height a rather good agreement with the experimental results is achieved. The strain distribution in the islands is then given by the finite element calculations, which are part of the simulation algorithm.