Optical properties of non-uniform thickness thin films of the glass-alloy system Cu-As-Se

Abstract

The optical constants and average thickness of metal-chalcogenide glass films of chemical composition CuxAs50Se50-x, with x = 5, 10 and 15 at.%, are accurately determined by a novel interferometric method, based on the optical transmission spectra at normal incidence, measured over the 300 to 2000 nm spectral region. This very useful optical method takes into account the non-uniform thickness of the layers. The dispersion of the refractive index is discussed in terms of the Wemple-DiDomenico relationship corresponding to the single-oscillator model. The optical absorption edges are described using the "non-direct transition" model proposed by Tauc, and the optical energy gaps are calculated by Tauc's extrapolation. It has been found that the value of the refractive index increases clearly with copper content whereas, on the contrary, the optical band gap decreases from 1.80 to 1.64 eV.