Influence of laser-irradiation on structural and optical properties of phase change Ga25Se75-xTex thin films

Ga25Se75-xTex chalcogenide thin films of thickness 400 nm were deposited by thermal vacuum evaporation technique. These films were irradiated by transversely-excited atmospheric-pressure (TEA) nitrogen laser for 15 min. As-prepared and laser-irradiated thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and UV/VIS/NIR spectroscopy. The XRD results revealed the amorphous nature of as-prepared films whereas, the laser-irradiated thin films showed the polycrystalline nature. The results were discussed in terms of the structural change, i.e. amorphous to polycrystalline phase change after laser irradiation. These structural changes were associated with the interaction of the incident photon and the lone-pair electrons, which affects the band gap of the Ga25Se75-xTex thin films. It was observed that the optical band gap decreases whereas, the absorption coefficient increases with increasing Te concentration and also inducing laser-irradiation. This decrease in the optical band gap was explained on the basis of changes in the structural behavior of films, i.e. from amorphous to polycrystalline state. (C) 2012 Elsevier B.V. All rights reserved.