We have investigated the strain and composition distribution in uncapped SiGe 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 scattering geometry at grazing incidence angles, but with high exit angles. The measured intensity distribution is compared to simulations based on the strain distribution calculated by a finite element method. Although pure Ge has been deposited during island growth by molecular beam epitaxy, the Ge composition varies from 0.5 at the island base to 1.0 at the top of the islands. Even at this top, the elastic relaxation reaches only about 50%.

Topics
Epitaxy, X-ray diffraction, Chemical vapor deposition, Finite-element analysis
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