Environmental Effects on the Electrical Characteristics of Back-Gated WSe2 Field-Effect Transistors

We study the effect of polymer coating, pressure, temperature, and light on the electrical characteristics of monolayer WSe2 back-gated transistors with Ni/ Au contacts. Our investigation shows that the removal of a layer of poly(methyl methacrylate) (PMMA) or a decrease of the pressure change the device conductivity from p-to n-type. From the temperature behavior of the transistor transfer characteristics, a gate-tunable Schottky barrier at the contacts is demonstrated and a barrier height of similar to 70 meV in the flat-band condition is measured. We also report and discuss a temperature-driven change in the mobility and the subthreshold swing that is used to estimate the trap density at the WSe2/SiO2 interface. Finally, from studying the spectral photoresponse of the WSe2, it is proven that the device can be used as a photodetector with a responsivity of similar to 0.5 AW(-1) at 700 nm and 0.37 mW/cm(2) optical power.