Optical properties of AsSe1.5−xTex glassy system

Thin AsSe_1.5−xTe_x films with 0x<1.5 have been prepared by a thermal vacuum evaporation technique onto quartz and glass substrates kept at room temperature (300 K). The optical constants, the refractive index, n, and the absorption index, k, of the films were determined for the investigated compositions of different thickness values (100–300 nm) using spectrophotometric measurements of the transmittance, T, and the reflectance, R, at normal incidence in the spectral range 400–2500 nm. The obtained values of both n and k were found to be independent of the film thickness within the above mentioned thickness range. The estimated indirect and direct optical energy gap decreased as tellurium content increased in the parent sample AsSe_1.5. The values of dispersion energy, E_d, and lattice dielectric constant, _L, of the system have been determined and correlated with the type and amount of chemical bonds and the relative proportion of the constituent elements in the examined compositions.