OPTICAL-PROPERTIES OF TIN DISELENIDE FILMS

SnSe2 films were deposited on substrates at 300 K by a conventional thermal evaporation technique. The as-deposited films were amorphous and transformed to the crystalline phase on post-deposition annealing above 573 K in an inert atmosphere. The optical properties of the films were investigated, using spectrophotometric measurements of the transmittance and reflectance at normal incidence in the wavelength range 400-2000 nm. The refractive index data fit a single oscillator model with a dispersion parameter 5.149 x 10-(14) and 5.773 x 10(-14) eV m2 for the amorphous and crystalline films, respectively. The high-frequency dielectric constant of the amorphous films decreased from 9.871 to 7.475 for the crystalline films. The analysis of the spectral behaviour of the absorption coefficient in the intrinsic absorption region revealed an indirect forbidden and a direct allowed transition with energy gaps 0.99 and 2.05 eV for the amorphous films and 0.96 and 2.02 eV for the crystalline films, respectively.