Optical properties of dense thin-film Si and Ge prepared by ion-beam sputtering

Abstract

The optical properties of ion-beam-sputtered Si and Ge have been measured using spectroscopic ellipsometry over the range of 2.5–5.0 eV. Measurements have been performed on films prepared at different substrate temperatures (Ts) . An analysis of the spectroscopic ellipsometry data using the Bruggeman effective medium approximation reveals that very dense polycrystalline Si ( p-Si) and Ge ( p-Ge) films are obtained (without postdeposition heat treatment) for Ts ≥350 °C and Ts ≥200 °C, respectively. Maintaining a sufficiently high Ar beam voltage in the sputtering process is shown to be beneficial to the densification of p-Si. Discrepancies observed between the structure of the p-Si deduced from Raman and ellipsometry spectra are also addressed. The ellipsometry data are effective in detecting heterogeneity possibly due to surface roughness for the p-Ge.