Optical properties of tin-selenid films

SnSe thin films of different thicknesses were prepared by the thermal evaporation technique in vacuum of 10−4 Pa. The structure analysis of the films as determined from the electron diffraction pattern and X-ray diffraction indicate that the films were polycrystalline of orthorhombic structure. The transmittance and reflectance of SnSe films were measured at normal incidence in the wavelength range of 760–2200 nm. It was found that the refractive index n and the absorption index k are independent of the film thickness. Graphical representation of log(α) as a function of (1/λ) shows two distinct linear parts indicating the existence of two optical transitions. The analysis of the spectral behavior of the absorption coefficient in the intrinsic absorption region revealed an indirect and direct allowed transition with energy gaps Egind = 0.895 eV and Egd = 1.27, respectively.