Interfacial roughness of Si1-xGex/Si multilayer structures on Si(111) probed by x-ray scattering

Interface structures in Si0.9Ge0.1/Si heterostructures and superlattices grown on vicinal Si(111) substrates are studied using x-ray reflectivity and diffuse scattering. A set of diffuse scattering data collected from a heterostructure sample were simultaneously fitted to a distorted-wave Born approximation calculation, giving a r.m.s. roughness in good agreement with those from reflectivity data, except for the top oxide layer, with a large out-of-plane correlation length of 460 Angstrom. A modified correlation function was introduced to account for the differential correlation between long- and short-wavelength roughnesses. Strong diffuse peaks are observed in rocking scans on a ten-period Si0.9Ge0.1/Si superlattice, revealing the structure of the miscut substrate to be highly replicated through subsequent overlayer growth of the Si and SiGe layers. The structure consists of surface terraces separated by bunched steps 41 Angstrom high. The correlation of successive layers is slightly misoriented from the surface normal, as is evident from the splitting in the specular and diffuse scattering peaks.