Effect of SnCl2 heat treatment on SnS thin films deposited by RF sputtering

Abstract

In this study, the effect of SnCl2 treatment on SnS thin films was investigated. SnS thin films were grown by RF sputtering and SnCl2 treatment was applied by wet chemical processing. The samples grouped as SnCl2 heat treated, annealed, as dep. were subjected to annealing in air atm. The as dep. sample grew in the orthorhombic SnS phase. Annealing of the SnS sample in air environment led to the formation of orthorhombic SnS as well as non-dominant SnS2 and SnO2 phases. It was found that applying SnCl2 heat treatment to SnS deteriorated the crystallization and especially the SnO2 oxide phase became more dominant. Raman spectra confirmed the presence of SnS and SnS2 phases in the samples, but no evidence of SnO2 phase was found. SEM images showed bladelike, dense grain formation in the as dep. and annealed samples. However, SnCl2 heat treatment completely changed the surface morphology of the sample, causing it to transform into a structure consisting of several domains split by deep fractures. EDS revealed a distinct Sn-rich composition of the as dep. and annealed samples (Sn/S~1.2). On the other hand, SnCl2 heat treatment caused a massive loss of sulfur in the atomic distribution of the SnS and it was seen that the Sn/S ratio increased to around 7.5. The band gaps of the as dep. and annelaed samples were calculated as 1.43 eV and 1.45, respectively. However, SnCl2 heat treatment led to an increase to 1.56 eV of the band gap. Analysis results show that SnCl2 treatment by the wet processing causes a significant change on the characteristics of SnS thin film. In this context, it can be said that SnCl2 heat treatment can be further improved with optimization processes.