Spectroscopic ellipsometry and X-ray diffraction studies on Si1-xGex/Si epifilms and superlattices

Comprehensive optical and structural properties are reported on several MBE grown thin Si1-xGex epifilms and Si1-xGex/Si superlattices with low Ge contents by using spectroscopic ellipsometry (SE), high resolution x-ray diffraction (HR-XRD) and Raman scattering (RS). For thin Si1-xGex films, our appraised results of the optical dielectric functions from SE spectra fitted to the parameterized models have revealed discrepancies with the existing data. While E1 and E1 + Δ1 critical point energies have shown similarities, their amplitudes uncovered ∼25% larger value for the E1 band-edge, and ∼10% larger value for the E1 + Δ1 band-edge. In our samples, the observed vibrational peaks in the RS are classified as unstrained SiSi, GeGe and GeSi modes. These mode assignments in Si1-xGex alloys are evaluated compared and discussed with the available RS data.