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

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