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 degreesC, the CuS layer converts to Cu8S5, which reacts with the underlying SnS thin film at about 400 degreesC 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 Omega(-1) cm(-1).