Preparation of SnS2 thin films by conversion of chemically deposited cubic SnS films into SnS2

We report the growth of SnS2 thin films by annealing chemically deposited cubic SnS films under a sulfur atmosphere in a graphite box. The chemically deposited SnS films were annealed in the temperature range of 200-550 °C to understand its influence on the conversion of SnS into SnS2. In the X-ray diffraction analysis, the as-deposited SnS films annealed in the temperature range of 200-250 °C showed the formation of a minor SnS2 phase along with the dominant SnS phase. The films annealed at 300 °C contained mixed phases of SnS and SnS2. Increasing the annealing temperature from 350 to 500 °C led to the formation of only the dominant SnS2 phase. Further increasing the annealing temperature to 550 °C gave rise to the formation of a highly oriented SnS2 film with hexagonal structure having (001) as the preferred orientation. The crystallite size of the SnS2 films was found to increase from 17 nm to 25 nm with increasing annealing temperature from 350 °C to 550 °C. The lattice parameters were found to be a = 0.365 nm and c = 0.592 nm. Raman spectroscopy analysis confirmed the formation of single phase SnS2 films at annealing temperatures above 350 °C. The morphological studies showed the conversion of the round shaped grains into flake-like ones on annealing at temperatures above 350 °C. These flakes increased in size on increasing the annealing temperature from 350 °C to 500 °C. The direct optical band gap of these SnS2 films was found to be 2.58 eV.