OPTICAL PROPERTIES OF GexAsxSe1-2x GLASSES

The optical properties of amorphous GexAsxSe2-x (x=0.05 divided by 0.30) thin films prepared by thermal evaporation on the glass substrates held at T-substr=100 degrees C are reported. The transmission spectra was used for calculation of the absorption coefficient alpha, optical band gap E-g, and the values of the refractive index n. The dependences of alpha, E-g, and n on the film composition in the GexAsxSe2-x glassy system were determined. It was established that the optical band gap Eg decreases, while the refractive index n increases with the increasing of the concentration of Ge and As in the GexAsxSe2-x glassy system. The time dependence of the transmission T(t) during the light exposure for the above band gap illumination (photodarkening) is described by a strength exponential behaviour T(t)/T(0) = A(0)+Aexp[-(t-t(0))/tau]((1-beta)), where t is the exposure time, tau is the apparent time constant, A characterizes the exponent amplitude, t(0) and A(0) are the initial coordinates, and beta is the dispersion parameter (0 <beta < 1).