Influence of Composition on Optical Constants and dc Conductivity of Se52In48-xPbx Thin Films

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. The temperature dependence of dc conductivity σ for the as deposited films of Se52 In48-xPbx in the temperature range (303 – 423 K) was recorded. For these films, it is suggested that the conduction is due to thermally activated process through the extended states. The effect of composition on the preexponential factor so and the activation energy DE were studied. It is found that the values of so and DE decreases with increasing Pb content (x = 28, 31, and 36 at. %) but for higher concentration of Pb (x = 40 at. %) so and DE were increased.