Thickness dependent physical properties of close space evaporated In_2S_3 films

摘要

In recent years, In_2S_3 is considered as a promising buffer layer in the fabrication of heterojunction solar cells. Film thickness is one of the important parameters that alters the physical characteristics of the grown layers significantly. The effect of film thickness on the structural, morphological, optical and electrical properties of close space evaporated In_2S_3 layers has been studied. In_2S_3 thin films with different thicknesses in the range, 100-700 nm were deposited on Corning glass substrates at a constant substrate temperature of 300 deg C. The films were polycrystalline exhibiting strong crystallographic orientation along the (103) plane. The deposited films showed mixed phases of both cubic and tetragonal structures up to a thickness of 300 nm. On further increasing the film thickness, the layers showed only tetragonal phase. With increase of film thickness, both the crystallite size and surface roughness in the films were found to be increased. The optical constants such as refractive index and extinction coefficient of the as-grown layers have been calculated from the optical transmittance data in the wavelength range, 300-2500 nm. The optical transmittance of the films was decreased from 82% to 64% and the band gap varied in the range, 2.65-2.31 eV with increase of film thickness. The electrical resistivity as well as the activation energy was evaluated and found to decrease with film thickness. The detailed study of these results was presented and discussed.