Strain and composition distribution in uncapped SiGe islands from x-ray diffraction

We have investigated the strain and composition distribution in uncapped Si Ge islands grown on Si (001) by x-ray diffraction. In order to be sensitive to the dot layer on the sample surface, and at the same time being able to measure in-plane strain and strain in growth direction, we utilized a scat tering geometry at grazing incidence angles, but with high exit angles. The measured intensity distribution is compared to simulations based on the st rain distribution calculated by a finite element method. Although pure Ge h as been deposited during island growth by molecular beam epitaxy, the Ge co mposition varies from 0.5 at the island base to 1.0 at the top of the islan ds. Even at this top, the elastic relaxation reaches only about 50%. (C) 20 01 American Institute of Physics.