Characterization of As-Se-Tl films near infrared region

?Amorphous chalcogenide of As-Se-Tl glassy alloys was prepared by melt quenching technique. Films were deposited on a transparent glass substrate using thermal evaporation technique. The optical characterization of thin As-Se-Tl films was studied by the analysis of transmission spectra, measured at normal incidence, in the spectral range 200-3000. The envelope method, proposed by Swanepoel, is a commonly used method for studying optical properties of films with uniform and non uniform thickness. Thickness values as well as optical constants, refractive index, Dispersion energy, Urbach and static refractive index or infinite wave length dielectric constant, are calculated using Wemple-DiDomenico model near infrared region using the envelopes of the transmittance spectrum of the films. The values of optical constants: absorption coefficient, Urbach tail, refractive index etc. have been determined. Urbach tail is estimated using Tauc's extrapolation and is found to increase from 0.69 to 0.91 eV with the Tl addition. This behavior of Urbach tail is interpreted in terms of Tauc's Model. Other optical constants are interpreted in terms of Wemple-DiDomenico model, chemical bond approach, electro-negativity difference of the atoms involved and cohesive energy of the system.