Structural, linear and non-linear optical properties of annealed and irradiated Ag/Se heterostructure films for optoelectronic applications

The present work demonstrates the effect of annealing and laser irradiation on the linear, nonlinear optical properties as well as the structural properties of thermally deposited Ag/Se bilayer thin films. The Ag diffusion into the Se layer by thermal annealing (annealed at 90 degrees C) and laser irradiation (532 nm) brings the changes which have been investigated. The structure of the studied films has been studied by X-ray diffraction and the surface morphology by field emission scanning electron microscopy. The optical transmission data of the films was collected from UV-vis-NIR spectrophotometer in the wavelength range 500-1200 nm. The refractive index (n) and extinction coefficient (k) were observed to be increased with photo thermal treatment. The indirect allowed optical band gap decreases with Ag diffusion as the width of the localised states increased. The dispersion of refractive index was analysed in terms of single oscillator Wemple-Di Domenico model. The third order nonlinear susceptibility (chi((3))) and nonlinear refractive index (n(2)) were calculated from the linear parameters using semi-empirical relations. The changes in the optical parameters with annealing and laser irradiation were explained on the basis of defect states and density of localised states due to Ag diffusion into Se matrix. The Raman study reveals the vibrational bonding information in the films. The tuneable optical properties can be used in various optoelectronic applications.