X-Ray scattering investigation of the interfaces in Si/Si 1− xGe x superlattices on Si(001) grown by MBE and UHV-CVD

Abstract

We have used X-ray scattering techniques to compare the interface quality in similar Si/Si 1− x Ge x superlattices on Si(001) grown by either molecular beam epitaxy (MBE) or ultra-high vacuum chemical vapor deposition (UHV-CVD). High-resolution X-ray diffraction revealed that both structures were fully strained. The superlattices grown by chemical vapor deposition showed less thickness fluctuations from period to period, but the interfaces were slightly less chemically abrupt than that of the corresponding molecular beam epitaxy-grown structure. Grazing incidence X-ray specular and diffuse scattering revealed significant differences in the microstructural properties of the interface roughness. Transverse rocking scans of satellite peaks and detector scans showed a very different diffuse component in MBE and UHV-CVD. The structure grown by MBE is characterized by a long auto-correlation length (0.5 μm) while the UHV-CVD sample possess a shorter correlation length (20–50 nm). In both cases, offset reflectivity scans showed that the diffuse scattering peaks at values of perpendicular wave vector transfer corresponding to the superlattice satellite peaks, indicating a strong cross-correlation of the interface roughness.