Optical characterization of vacuum evaporated a-Se80Te20−xCux thin films

Thin films of a-Se80Te20−xCux (where x=2, 6, 8 and 10) were deposited on glass substrates by vacuum evaporation technique. The absorbance, reflectance and transmittance of as-deposited thin films were measured in the wavelength region 400-1000 nm. The optical band gap and optical constants of amorphous thin films have been studied as a function of photon energy. The optical band gap increases on incorporation of copper in Se80Te20−xCux system. The value of refractive index (n) decreases while the value of the extinction coefficient (k) increases with increasing photon energy. The results are interpreted in terms of concentration of localized states.