Structural and optical properties of thermally evaporated Se55Ge30As15 thin films

Chalcogenide glass Se55Ge30As15 have amorphous structure in both as-deposited and annealed conditions. The optical properties of the as-deposited and annealed films were studied using spectrophotometric measurements of transmittance, T(lambda), and reflectance, R(lambda), at normal incidence of light in the wavelength range 200-2500 urn. Neither annealing temperature nor film thickness can influence spectral response on refractive index and absorption index of films. The type of electronic transition responsible for optical properties is indirectly allowed transition with energy gap of 1.94 eV and phonon energy of 40 meV. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple-Didomenico (WD) model. The width of band tails of localized states into the gap (Delta E), the single oscillator energy (E-o), the dispersion energy (E-d), the optical dielectric constant (epsilon(infinity)), the lattice dielectric constant (epsilon(L)) the plasma frequency (omega(p)) and the free charge carrier concentration (N) were estimated. (c) 2005 Elsevier Ltd. All rights reserved.