Effects of heat treatment on the optical and structural properties of InSe thin films

Thin films of indium selenide of different thicknesses are deposited on glass substrate by vacuum evaporation. The optical gaps (Egopt) are determined from the absorption spectra of as-deposited InSe films. The value of Egopt of a-InSe films is found to increase with the thickness of the films. The InSe films are heat treated at different elevated temperatures from 423 to 573 K. The values of optical gaps Egopt of InSe films are also found to increase with temperature of heat treatment. The effect of thickness and temperature of heat treatment on the optical gap (Egopt) of the film is interpreted in terms of the density of state model of Mott and Davis. The valence and density of states of a-InSe films is calculated from the optical absorption data. The variation of valence band density of states with temperature of heat treatment is observed in the case of a-InSe films. X-ray diffraction spectra are taken for both, as-deposited and heat treated InSe films. A radial distribution function (RDF) analysis of X-ray diffraction (XRD) spectra is made to RDFs of the specimens it is shown that in case of InSe a transition from the amorphous to the crystalline state takes place at 573 K. (author)