Influence of composition on optical constants and dc conductivity of Se52In48-xPbx thin Films

Abstract

Thin films of Se52In48-xPbx (x = 28, 31, 36 and 40 at. %) were deposited under vacuum (10-5 Torr) on glass substrates by thermal evaporation technique of the bulk compounds. The optical ‎transmission and reflection spectra of these films were measured in the range 1000 - 2200 nm ‎and the optical constants (absorption coefficient α, refractive index n, extinction coefficient k, real εr and imaginary part εr of the dielectric constant) were calculated for Se52In48-xPbx ‎compositions films as a function of photon energy (hυ). The absorption data revealed the existence of ‎allowed direct and indirect transitions. It has been found that the optical band gap Eg decreases ‎with increasing Pb content up to x = 36 at.% then, increases as Pb content raised up to 40 at%.‎The results were interpreted in terms of the change in the average band energy of the films as a ‎function of composition. The increase of the optical energy gap at x = 40 at.% which allows to the decrease in density of localized ‎states in the band gap.‎