Influence of thermal annealing on optical constants of Ag doped Ga–Se chalcogenide thinfilms

The effect of thermal annealing on the structural and optical properties of Ag doped Ga–Se chalcogenide thin films has been studied. It is found that the films partially transform from amorphous to crystalline phase. The X-ray diffraction technique and FESEM have been used to study the transformed phases. The effect of thermal annealing on the optical spectrum of these thin films has been studied in the wavelength spanning from 450 to 1100 nm. It is found that the calculated optical band gap (Eg) decreases while the absorption coefficient and extinction coefficient increases with increasing the annealing temperature. The film transparency decreases with increasing annealing temperature. The decrease in the optical band gap has been explained on the basis of change in nature of the films, from amorphous to polycrystalline state, with increasing the annealing temperature.