Yielding Enhanced Gas Sensing in WO3 Thin Films via p-n Heterojunction Formation

Semiconductor nanostructures have attracted considerable attention for developing high-performance gas sensors for the high-level detection of highly flammable and toxic gases. Herein, the present work integrates n-type WO3 with p-type Ag2O to form a p-n heterojunction by DC reactive magnetron co-sputtering technique. The CH4 sensing performance of the p-n heterojunction with Ag content is correlated with the crystalline structure, surface morphology, elemental composition, optical band gap, and chemical states of the thin film. The p-n heterojunction thin film with 3.63 at. % Ag exhibits a maximum CH4 sensitivity of 70.61 % towards 25 ppm at a low operating temperature of 75 °C. The optimised CH4 sensor also demonstrates a fast response/recovery time of 28 s/106 s with a low detection limit of 1 ppm, excellent repeatability, and long-term stability. The effectiveness of the p-n heterojunction is validated by comparing the sensing performance with that of pristine n-type WO3. Moreover, the utilisation of our optimised p-n heterojunction thin-film-based sensor is further extended towards CO, H2S, H2 and NH3 gas detection, with a detection limit of 25 ppm. This easily implementable approach to designing p-n heterojunctions could pave the way for advanced next-generation sensing technology.