Photogating in few-layered ReS₂ Phototransistors

Two-dimensional layered transition metal dichalcogenides (TMDs) have shown much promise due to their remarkable electro-optical properties and potential uses as photodetectors. We measured the photoconductivity on few-layered (≤ 10 layers) ReS₂ field-effect transistors (FET) in both two-terminal and four-terminal configurations using a 532 nm excitation source. The photocurrent was measured as a function of incident optical power, drain-source voltage, and back-gate voltage. We obtained a maximum responsivity (R) of 45 A/W corresponding to an external quantum efficiency (EQE) of ~10,500% in the four-terminal configuration. We also observed photogating, in which varying the incident optical power shifts the FET threshold voltage. We will present our results and discuss their implications for the presence of trap states and the effect on the overall channel carrier density.