Abstract
This study investigates the effects of substitution of selenium by sulfur on the optical constants of amorphous (a-)As20Se80-xSx films (x=0, 4, 8, 12, 16, and 20at%), where the coordination number for both Se and S is the same. The absorption coefficient, , and the index of refraction, n, were derived using the transmission spectra in a wide range of wavelengths from 400 to 2500nm. This revealed that the index of refraction for the a-As20Se80-xSx system decreases with increase in sulfur content throughout the range under study. The effective coordination number of As has been determined based on the refractive index dispersion analysis. A decreasing in N-c from 4.022 to 3.752 with increase content of sulfur from 0 to 20at% has been recorded. In addition, the optical bandgap, E-g, of the a-As20Se80-xSx thin films increases with increase in S content which can be explicated in terms of the chemical bond approach.