Photoinduced effect in nanostructured InSe thin films for Photonic applications

Nanostructure InSe thin films were prepared using thermal evaporation technique under a vacuum of 10−4 Pa onto a cleaned quartz substrate at room temperature, and then exposed to UV illumination. Structural analysis of the films confirmed that the virgin films have an amorphous background with a preferential orientation in the (002) direction. It is found that the UV illumination resulted significant changes in the microstructure of these films. It is observed that the values of crystallite size decrease on increasing illumination time. The optical parameters were obtained using spectrophotometric measurements of the transmittance and reflectance at normal incidence of light in the wavelength range of 200–2500 nm. The type of optical transition was found to be an indirect allowed transition and the optical energy gap decreases (photo-darkening) with the increase of UV exposure time. The dispersion of the refractive index has been discussed in terms of Wemple-Didomenico single oscillator model.