Different compositions of amorphous Ge15Se85-xCux thin films were deposited onto glass substrates by
the thermal evaporation technique. Their amorphous structural characteristics were studied by X-ray
diffraction (XRD). The optical constants (n, k) of amorphous Ge15Se85-xCux thin films were obtained by
fitting the ellipsometric parameters (j and D) data for the first time using three layers model system in
the wavelength range 300e1100 nm. It was found that the refractive index, n, increases with the increase
of Cu content. The possible optical transition in these films is found to be indirect transitions. The optical
energy gap decreases linearly from 1.83 to 1.44 eV with increasing the Cu. The experimental transmittances
spectrum can be simulated using the thickness and optical constants modeled by spectroscopic
ellipsometry model.