Optical Properties of Amorphous Silicon–Carbon Alloys (a-Si x C1-x ) Deposited by RF Co-Sputtering

Abstract

Amorphous silicon–carbon alloy (a-SixC1-x) thin films have been deposited by radio frequency (RF) sputter deposition. These films were obtained, from a composite target consisting of silicon fragments regularly distributed on the surface of a pure graphite disc, for different values of silicon surface fraction RSi/C, at an RF power of 250 W. X-ray diffraction diagrams show that all the as-deposited SixC1-x thin films are amorphous. The optical properties of the a-SixC1-x films were investigated by optical transmission measurements in the ultraviolet–visible–near infrared wavelengths range. The optical band gap Eg varies, with RSi/C, from 1.4 to 1.9 eV and presents a wide maximum at an RSi/C value of about 35 %. This maximum value is attributed to amorphous silicon carbide a-SiC as confirmed by theoretical correlation between the molar fraction x and RSi/C. The refractive index n follows well the Cauchy law and the extrapolated value, at infinite wavelengths, increases from 2.1 to 2.65 as the RSi/C fraction increases.