Effect of Sn content on some optical properties of Se90Pb10-x thin films

Se90Pb10 and Se90Pb8Sn2 thin films of thickness 400 nm were evaporated on glass substrates. The glassy nature of the prepared films was ascertained by differential scanning calorimeter thermograms and X-ray diffraction patterns. Spectra of reflection and transmission of the prepared films were recorded using FilmTek3000 in the wavelength range of 300-900 nm. The absorption coefficient was calculated and used to evaluate the optical band gap energy which comes out to be 2.1 and 2.2 eV for SePb and SePbSn thin films, respectively. The extinction coefficient (k), refractive index (n), real (epsilon') and imaginary (epsilon") dielectric constants were also obtained. Results indicate that the addition of Sn content reduces the value of (n), (epsilon') and (epsilon"), while that of k increases. The observed changes in the studied optical parameters were interpreted depending on the chemical bond approach of Tichy and Ticha.