Large and small angle x-ray scattering studies of Si/SiGe superlattices grown by gas-source molecular beam epitaxy

Abstract

We have performed large and small angle x-ray scattering measurements on Si/Si0.7Ge0.3 superlattices grown by gas-source molecular beam epitaxy. The thickness of the Si and SiGe layers as well as their Ge content were extracted through a correlation between large-angle x-ray diffraction and photoluminescence measurements. A SiGe growth rate enhancement was observed during the first stages of the SiGe layer deposition, which might be due to a slow build-up of the Ge surface population. The Fresnel optical method was used to analyse the small-angle specular x-ray reflectivity data. The interface root mean square roughness, 7 ± 1 Å for the samples grown at 520 and 580 °C, and 5 ± 1 Å for the sample grown at 550 °C, are quite comparable to those found in Si/SiGe superlattices grown by solid source MBE. The crystallographic quality of those stackings is very good; no measurable period dispersion has been obtained in x-ray diffraction.