Crystalline phase change and improvement in electro-optical parameters of SnSx thin films by different ambients

SnSx thin films were deposited on glass substrates by sol–gel spin coating technique. The effects of various annealing ambients such as air, O2, Ar and N2 on structural, morphological, optical and electrical properties of thin films were investigated. X-Ray diffraction (XRD) results showed that the annealed sample in the air has the tetragonal SnO2 phase, while by annealing of the sample in O2, Ar and N2 the hexagonal SnS2 and the orthorhombic SnS structures were formed and the SnS to other phase fraction increased by Ar annealing. Field emission scanning electron microscopy (FESEM) images displayed that the film surface is constituted by homogeneously distributed nanograins and Ar annealing enhances the particle size. Transmittance spectra indicated that Ar and N2 annealing remarkably reduced the transparency of films and led to redshift of the optical absorption edge so that the band gap reduced from 3.69 in air-annealed films to 2.42 in N2-annealed films. The optical constants of thin films were estimated by envelope method. The PL spectra of air- and O2-annealed thin films exhibited the blue emission, while the N2 and Ar annealing causes green emission. Hall effect measurements revealed that the annealing of films in N2 leads to highest mobility compared to the other samples, whereas the carrier concentration and conductivity of SnSx thin films show the best electrical results which has been annealed in Ar ambient.