Ellipsometry and optical measurements on amorphous thin films of As2Se3

Thin films of amorphous AsSe_3/2 have been prepared by thermal evaporation of the material under a vacuum of 1.33×10^?3 Pa. Reflectivity, transmission and ellipsometric measurements of the films have been carried out. The optical energy gap and the absorption coefficient as a function of wavelength were obtained. Two absorption bands were observed and interpreted in terms of defects in the AsSe_3/2 system (homopolar bonds). Analysis of reflection and transmission spectra shows that the electron density at band tails of both conduction and valency bands follows N(E)?E^1/2 (Taue plots). No considerable variations were observed on changing the film thickness.