Influence of grain size on the band-gap of annealed SnS thin films

•Fabrication of SnS thin films which were vacuum annealed post deposition.•Films were polycrystalline with the unit cell size independent of thickness.•Unit cell size was also independent of annealing temperature.•Only the grain size was found to vary.•The band-gap and refractive index were found to be dependent of the grain size.

Thin films of SnS were fabricated at room temperature on glass substrates by thermal evaporation. X-ray photo-electron spectroscopy confirmed that the films were stoichiometric in nature even after vacuum annealing. X-ray diffraction, Raman analysis and electron microscopy showed that the films were polycrystalline in nature with ortho-rhombic structure and preferred orientation. The only variation due to film thickness and annealing temperature was the grain size. Thus, this provided a chance to investigate the variation in optical properties as a function of the grain size. The energy band-gap and refractive index were estimated using UV-visible absorption spectra. The variation in band-gap with grain size showed blue-shift typical of electron quantum confinement. The effect of crystal ordering on refractive index was also evident by the linear increase of the refractive index with grain size.