Nanostructured MoS 2 and WS 2 Photoresponses under Gas Stimuli.

This study was on the optoelectronic properties of multilayered two-dimensional MoS 2 and WS 2 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, CO 2 , and O 2 environments at different flow rates. The electrical Hall effect measurement showed the existence of MoS 2 (n-type)/Si (p-type) and WS 2 (P-type)/Si (p-type) heterojunctions with a higher sheet carrier concentration of 5.50 × 10 5 cm -2 for WS 2 thin film. The IV electrical results revealed that WS 2 is more reactive than MoS 2 film under different gas stimuli. WS 2 film showed high stability under different bias voltages, even at zero bias voltage, due to the noticeably good carrier mobility of 29.8 × 10 2 cm 2 /V. WS 2 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 CO 2 environment was observed. Additionally, the external quantum efficiency of WS 2 revealed a remarkable enhancement in the CO 2 environment of 1.62 × 10 8 compared to MoS 2 film with 6.74 × 10 6 . According to our findings, the presence of CO 2 on the surface of WS 2 improves such optoelectronic properties as photocurrent gain, photoresponsivity, external quantum efficiency, and detectivity. These results indicate potential applications of WS 2 as a photodetector under gas stimuli for future optoelectronic applications.