Optical spectra of Si<i>x</i>Ge1−<i>x</i> alloys

Abstract

We report pseudodielectric functions of SixGe1−x alloys at room temperature, measured ellipsometrically on polycrystalline samples and single-crystal epitaxial layers, in the 1.7–5.6 eV range. Accurate values of the E1 threshold energies are obtained from numerically differentiated spectra. The measured dependence of E1 on x provides an efficient way to determine the alloy composition x. The spectral and compositional dependence of the optical constants forms a data base for optical studies of Si/SiGe layered structures.