Optical characterization of vapour-deposited amorphous As S Ag films

The transmittance spectra of the thermally evaporated As25S65Ag10 thin films were measured in the spectral range 300 to 900 nm. The analysis proposed by Swanepoel wR. Swanepoel, J. Phys. E 16 1983.1214x, enabling the determination of the refractive index n. and layer thickness d., has successfully been applied. The dispersion of n is discussed in terms of the single-oscillator Wemple and DiDomenico model. The energy of the single oscillator increases while the high-frequency dielectric constant decreases as a result of 1 h isothermal heating of the as-deposited films up to 450 K. The spectral dependence of the absorption coefficient of the films indicates that ‘non-direct transition’ is the responsible mechanism for the photon absorption. Crystallization of the orthorhombic arsenic sulphide As2S5.phase after thermal annealing at 470 K reduces the optical gap of the as-prepared film down to 1.41 eV. q1999 Elsevier Science B.V. All rights reserved.