Effect of Graphite as Electrodes on Electrical and Photoelectrical Behavior of Multilayer MoS2 and WS2 FETs

Transition-metal dichalcogenide materials have attracted considerable attention due to their outstanding properties, and however, the carrier collection efficiency remains a major problem for achieving high-performance electronic and optoelectronic devices. In this research, we compared the carrier transport properties of graphite and Au in contact with MoS ₂ (WS ₂ ) materials. The use of graphite for the drain–source electrodes significantly improves carrier collection efficiency, thus enhancing the overall electronic and optoelectronic performance of MoS ₂ and WS ₂ FETs. The device’s ON/ OFF current ratio with two graphite contact electrodes increased by about two orders of magnitude (120 and 207 for MoS ₂ and WS ₂ FETs, respectively) than that with conventional Au electrodes. Furthermore, the Gr-MoS ₂ -Gr FET shows ultrahigh responsivity (3869 A/W), detectivity ( $4.6\times10$ ¹² Jones), and extraordinary short photoresponse fall time ( $60 ~\mu \text{s}$ ). Compared with the Au-MoS ₂ -Au FET, the fall time is reduced by about six orders of magnitude. Interestingly, the Gr-MoS ₂ -Gr and Gr-WS ₂ -Gr FETs demonstrate different detection mechanisms. The Gr-MoS ₂ -Gr photodetector shows a photoconduction mechanism under the gate voltage of −10 to −6 V and a photogate mechanism under −4 to 2 V, whereas the Gr-WS ₂ -Gr photodetector is only driven by a photoconduction mechanism. The Gr-TMDs-Gr’s outstanding electronic and photoelectrical properties hold great potential for various applications in advanced optoelectronic devices.