Composition and strain of Ge domes on Si(001) close to the dome/susbtrate interface

Strain fields and composition gradient in epitaxial Ge dome-shaped islands grown on Si(001) substrates are determined by combining grazing-incidence multiwavelength anomalous diffraction and grazing-incidence diffraction anomalous fine-structure spectroscopy. This unique combination, together with numerical X-ray diffraction calculations carried out in the frame of the distorted-wave Born approximation with a structural model obtained by molecular dynamics, is shown to probe unambiguously the Ge composition even in the difficult region close to the island/substrate interface and to elucidate the vertical compositional profile inside the dome-shaped islands. A rather abrupt chemical composition profile close to the interface and a slight increase of the average Ge composition from the base to the top are observed for islands grown at a temperature of 650 degrees C. These experiments provide unique fundamental knowledge on the mechanism of Si-Ge intermixing during island growth, clarifying and quantifying the effects of growth conditions and morphology on the structural local properties of the nano-islands. Copyright (C) EPLA, 2011