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

Abstract

The step-bunching process during the growth on vicinal Sisubstrates provides a template both for improved lateral ordering and sizecontrol of the resulting Ge-rich self-assembled quantum dots or wires. Wehave investigated a 20 period SiGe/Si wire multilayer grown by molecularbeam epitaxy on a misorientated Si(001) substrate with a large miscut of3.5° 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. Inorder to get information on the shape and the lateral correlation not onlyof the wires on the top surface but also of the buried ones, we employedgrazing incidence small-angle x-ray scattering (GISAXS). The GISAXS datawere taken for different information depths in two orthogonal azimuths.Side maxima in coplanar high-angle diffraction and GISAXS data indicatethe presence of Ge-rich self-organized wires at the buriedheterointerfaces.