  We study the effect of polymer coating, pressure and temperature on the
electrical characteristics of monolayer WSe2 back-gated transistors with
quasi-ohmic Ni/Au contacts. We find that the removal of a layer of poly(methyl
methacrylate) or decreasing the pressure change the device conductivity from p
to n-type. We study the current-voltage characteristics as a function of the
temperature and measure a gate-tunable Schottky barrier at the contacts with a
height of 60 meV in flat-band condition. We report and discuss a change in the
mobility and the subthreshold slope observed with increasing temperature.
Finally, we estimate the trap density at the WSe2/SiO2 interface and study the
spectral photoresponse of the device, achieving a responsivity of 0.5 AW^-1 at
700 nm wavelength and 0.37 mWcm^-2 optical power.
