Nanostructured MoS₂ and WS₂ Photoresponses under Gas Stimuli

This study was on the optoelectronic properties of multilayered two-dimensional MoS₂ and WS₂ materials on a silicon substrate using sputtering physical vapor deposition (PVD) and chemical vapor deposition (CVD) techniques. For the first time, we report ultraviolet (UV) photoresponses under air, CO₂, and O₂ environments at different flow rates. The electrical Hall effect measurement showed the existence of MoS₂ (n-type)/Si (p-type) and WS₂ (P-type)/Si (p-type) heterojunctions with a higher sheet carrier concentration of 5.50 × 10⁵ cm^-2 for WS₂ thin film. The IV electrical results revealed that WS₂ is more reactive than MoS₂ film under different gas stimuli. WS₂ film showed high stability under different bias voltages, even at zero bias voltage, due to the noticeably good carrier mobility of 29.8 × 10² cm²/V. WS₂ film indicated a fast rise/decay time of 0.23/0.21 s under air while a faster response of 0.190/0.10 s under a CO₂ environment was observed. Additionally, the external quantum efficiency of WS₂ revealed a remarkable enhancement in the CO₂ environment of 1.62 × 10⁸ compared to MoS₂ film with 6.74 × 10⁶. According to our findings, the presence of CO₂ on the surface of WS₂ improves such optoelectronic properties as photocurrent gain, photoresponsivity, external quantum efficiency, and detectivity. These results indicate potential applications of WS₂ as a photodetector under gas stimuli for future optoelectronic applications.