Interface structure of Ge/Si(111) during solid-phase epitaxy studied by medium-energy ion scattering

The interface structure between a Ge thin film and Si(111) substrate during solid-phase epitaxy of Ge is studied by medium-energy ion scattering. Intermixing within the bilayer between the two-dimensional Ge layer with the critical thickness of 4 monolayers (ML) and the Si substrate occurs at 550 °C and above. The intermixing advances into deeper layers with annealing at higher temperatures, and Si atoms from the substrate migrate to the uppermost surface above 770 °C. When Ge is deposited, in excess of the critical thickness, three-dimensional islands form on the two-dimensional layer with a thickness of 4 ML before intermixing between Ge and Si layers begins. Atomic displacement is observed in both the Ge film and the substrate near the interface. The substrate is compressed vertically about 1.2%. However, the strain caused by the lattice mismatch between Ge and Si is relaxed by intermixing, so atomic displacement is partially restored.