Laser induced SnS2-SnS phase transition and surface modification in SnS2 thin films

Abstract

A thin film of SnS2 obtained by close-spaced vacuum sublimation was irradiated by an Nd:YAG laser (λ = 532 nm) using two intensities of laser radiation of 8.5 MW/cm2 and 11.5 MW/cm2. It was shown that laser irradiation leads to evaporation of sulphur from the surface, and the formation of SnS and Sn2S3 phases. The study of samples’ cross-section by energy dispersive X-ray analysis reveals that in the case of irradiation at 8.5 MW/cm2 intensity, the SnS layer is formed only at the surface of the initial SnS2 thin film. The application of more intensive radiation of 11.5 MW/cm2 leads to changes in chemical composition for the entire thin film. The formation of the predominant SnS phase, which includes a small amount of Sn2S3, was confirmed by the X-ray diffraction and Raman spectroscopy methods, as well as by measurements of optical reflectance and transmittance spectra. It was established that laser irradiation of the samples leads to the coalescence of grains accompanied by smoothing of the surface. The current-voltage characteristics of the ITO/SnxSy/Al samples show an ohmic behaviour in the case of non-irradiated intensity samples; for irradiated samples, the diode behaviour of I-V curves was observed. This is considered as evidence of the formation of p-SnS/n-SnS2 heterojunction by laser irradiation.