Optical properties and phase composition of α-C:H films

Abstract

The possibility of using α-C:H films for amorphous superlattices synthesis is investigated. For this purpose the dependence of optical properties on growth conditions as well as on film thickness is determined. The refractive index, n, extinction, k, and film thickness, d, are calculated from the measurement of light transmission and reflectivity in the range 0.85–3.5 eV. On the basis of the calculations, optical band gap of α-C:H films is estimated. It is shown that optical band gap is changed from 0.55 up to 1.9 eV and depends on deposition conditions. By means of effective medium approximation, it is shown that the optical properties of a film change with phase composition. It is found that the films contain diamond-like, graphite-like and polymer phases. Multilayer periodic structures based on the α-C:H films with different band gaps were synthesized. The thicknesses of the layers are in the range 8.0–25.0 nm. The optical properties and band gap of these structure are investigated. It is shown that these structures have two values for an optical band gap.