Thermal annealing of SnS thin film induced mixed tin sulfide oxides-Sn2S3 for gas sensing: Optical and electrical properties

This work reports the air-annealing effect on the structure, optical and electrical properties of tin sulfides (SnS) thin films and the capability of using these films for gas sensing application. The X-ray diffraction investigation shows that the predominant phase SnS (040) plane for the as-deposited film changes into Sn2S3 (201) plane after annealing. Furthermore, the annealed films at high temperatures (533 and 553 K) are partially oxidized leading to the formation of mixed tin sulfide oxides-Sn2S3 (MTO-Sn2S3) heterostructure thin film. The optical constants and thickness of films are calculated using Swanpole's method. Both optical band gap and electrical activation energy increased after annealing in the range (493-553 K) for 0.5 h in ambient air. Optical and electrical results indicate the existence of mixed phase characteristics of studied films. The gas sensing properties of MTO-Sn2S3 composite are investigated for methane gas detection. The fabricated sensor exhibits a weak sensitivity at low operating temperatures (50 and 100 °C). The sensitivity improves at high temperatures reaching its maximum at 250 °C. At 250 °C the response and recovery times are 250 and 82 s, respectively.