Optical properties of selenium-tellurium nanostructured thin film grown by thermal evaporation

Se-Te nanostructured thin films were deposited on glass substrates in the presence of oxygen and argon by thermal evaporation. The properties of Se-Te thin films strongly depend on the deposition method. During the process used, the substrate is cooled to a temperature of 77 K employing liquid nitrogen. The nanostructured thin films of Se_100−xTe_x (where x=4, 8 and 16) are deposited on glass substrate. The surface morphology of the deposited films was investigated through Scanning Electron Microscopy (SEM). The typical size of these nanostructures is in the range 40-100 nm and the length is of the order of several micrometers. The optical parameters i.e. optical gap (E_g), absorption coefficient (α), and extinction coefficient (k) are calculated in the wavelength range 190-1100 nm. It was found that the optical band gap decreased from 3.4 to 2.9 eV when Te concentration was increased in the Se_100−xTe_x nanostructured thin films. The large bandgap may be attributed to the decrease in particle size which clearly exhibits a quantum size effect. XRD analysis was performed to confirm glassy nature of the nanostructured thin films.