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Oxidation of Ultrathin SiGe Layer on Si(001): Evidence for Inward Movement of Ge

An ultrathin SiGe layer prepared by growing Ge epitaxially on Si(001) was oxidized and investigated using X-ray photoelectron spectroscopy (XPS) and medium energy ion scattering (MEIS). Growth at a substrate temperature 550° C leads to the formation of a mixed SiGe layer on Si(001). Oxidation of this sample at 250° C forms predominantly SiO2 and a small amount of GeO. MEIS shows evidence for the diffusion of Ge inwards by 2–3 Å and of Si towards the surface resulting in the pile up of Ge at the SiO2/SiGe interface. On annealing the oxidized surface at 360° C, oxygen leaves the Ge sites and form SiO2 thereby reducing GeO to elemental Ge. The concentration of oxygen remains the same through out this reaction.