Copper tin sulfide semiconductor thin films produced by heating SnS–CuS layers deposited from chemical bath

Copper tin sulfide (Cu₄SnS₄) thin films have been prepared by heating a layer of CuS thin film deposited over an SnS thin film, both obtained by chemical bath deposition. Upon heating in a nitrogen atmosphere at 300–340 °C, the CuS layer converts to Cu₈S₅, which reacts with the underlying SnS thin film at about 400 °C to form Cu₄SnS₄. The optical band gap of Cu₄SnS₄ has been found to be approximately 1 eV, involving direct forbidden transitions. The films are photosensitive, and the electrical conductivity in the dark is about 1 Ω⁻¹ cm⁻¹.