Abstract
Thermal evaporation technique was used to prepare a-Ge70Se30 thin films onto glass substrates of thicknesses range (108-717 nm). Transmittance measurements in the wavelength range (400-2500nm) were used to calculate the refractive index n and the extinction coefficient k using Swanepole's method. The calculated parameters such as optical band gap E-g(opt), the width of the tail of localized states in the band gap E-e, optical conductivity sigma(opt), complex dielectric constant, relaxation time tau and dissipation factor tan delta were determined. The analysis of the optical absorption data revealed that the optical band gap E-g(opt) was indirect transitions. The optical dispersion parameters E-o and E-d were determined according to Wemple - DiDomenico method.