The dependence of optical parameters on composition in the GexAsxSe1-2x glassy system

Abstract

The optical properties of amorphous GexAsxSe2-x (x = 0.050.30) thin films prepared by thermal evaporation on glass substrates held at Tsubstr = 100 oC are reported. The transmission spectra was used for the calculation of the absorption coefficient , optical band gap Eg, and the values of the refractive index n. The dependences of , Eg, and n on the film composition in the GexAsxSe1-2x glassy system were determined. It was established that the optical band gap Eg decreases, while the refractive index n increases with increasing 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 behavior T(t)/T(0) = A0 Aexp[-(t-t0)/τ] (1-) , where t is the exposure time, τ is the apparent time constant, A characterizes the exponent amplitude, t0 and A0 are the initial coordinates, and  is the dispersion parameter (0