Grazing incidence X-ray scattering from Ge/Si superlattices grown at low temperature

Grazing incidence X-ray specular and off-specular scattering has been used to determine the structure of interfaces in Ge/Si superlattices grown by molecular beam epitaxy. At low growth temperature, for large Ge layer thickness an asymmetry was observed in the interface width, that of the Si layer becoming very large. When this was observed, the measured Ge layer thickness was substantially less than the nominal thickness determined from the growth parameters. X-ray diffuse scattering measurements show that the topological roughness was small. The data are interpreted in terms of diffusion of Ge into the Si beneath the Ge layer, a modified Stranski–Krastanov growth mode resulting in the formation of a 3-dimensional “inverted hut” structure of Si–Ge islands. Grazing incidence X-ray scattering provides a rapid and non-destructive technique for the identification of the growth mode.