Influence of thickness on structural and optical properties of evaporated SnS films

SnS films with thicknesses of 65-580 nm have been deposited on glass substrates by thermal evaporation. The physical properties of the films were investigated using X-ray diffraction, scanning electron microscopy, and ultraviolet-visible-near infrared spectroscopy measurements at room temperature. It indicates that the deposited films mainly exhibit SnS phase, but they contain tiny SnO₂. The deposited SnS films are pinhole free, smooth and strongly adherent to the surface of the substrate. With the increase of the film thickness from 65 nm to 580 nm, the color of the SnS films changes from brown to dark brown to grey, and the grains of the films become larger and larger, and the direct bandgap and indirect bandgap decrease. All the films have larger direct bandgap of 1.55 - 2.30 eV, which is much larger than 1.3 eV of bulk SnS, and indirect bandgap of 1.10 - 1.29 eV.