Environmental Effects on the Electrical Characteristics of Back-Gated WSe ₂ Field-Effect Transistors

Abstract

We study the effect of polymer coating, pressure, temperature, and light on the electrical characteristics of monolayer ${\mathrm{WSe}}_2$ back-gated transistors with $\mathrm{Ni}/\mathrm{Au}$ 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 $~$ 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 ${\mathrm{WSe}}_2{/\mathrm{SiO}}_2$ interface. Finally, from studying the spectral photoresponse of the ${\mathrm{WSe}}_2$ , it is proven that the device can be used as a photodetector with a responsivity of $~0.5{\mathrm{AW}}^{-1}$ at $700\mathrm{nm}$ and $0.37\mathrm{mW}/{\mathrm{cm}}^2$ optical power.