Optical energy gaps of β-In2S3 thin films grown by spray pyrolysis

β-In2S3 thin films for which x varied from 2.0 to 3.9 with the x composition of the spray solution (In2Sx) were grown on thoroughly cleaned glass slides by the spray pyrolysis method with the substrate temperature maintained at 350 °C and a rate of spray of 6 ml/min. The energy gap of the grown β-In2S3 thin film was 2.20 eV, indicating an indirect transition, whereas that of In2S3.9 increased to 2.43 eV.