Influence of thickness on structural and optical properties of evaporated tin sulphide films

Tin sulphide (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, atomic force microscopy, Raman spectroscopy and ultraviolet-visible-near-infrared spectroscopy measurements at room temperature. It is indicated 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 to 580 nm, the colour of the SnS films changes from brown to dark brown to grey, and the grains and roughness of the films become larger and larger, but the direct bandgap decreases. All the films have larger direct bandgap of 1.55-2.28 eV, which is much larger than the 1.3 eV of bulk SnS.