X-ray studies on self-organized wires in SiGe/Si multilayers

The step-bunching process during the growth on vicinal Si substrates provides a template both for improved lateral ordering and size control of the resulting Ge-rich self-assembled quantum dots or wires. We have investigated a 20 period SiGe/Si wire multilayer grown by molecular beam epitaxy on a misorientated Si(001) substrate with a large miscut of 3.5° towards the [100] direction. Parallel to the steps, i.e. along the [010] direction, Ge-rich wires are formed spontaneously. Their surface morphology was studied with atomic force microscopy. In order to get information on the shape and the lateral correlation not only of the wires on the top surface but also of the buried ones, we employed grazing incidence small-angle x-ray scattering (GISAXS). The GISAXS data were taken for different information depths in two orthogonal azimuths. Side maxima in coplanar high-angle diffraction and GISAXS data indicate the presence of Ge-rich self-organized wires at the buried heterointerfaces.