Phonon-Limited Electron Transport in Back-Gated Few-layer MoSe$_2$ Field- Effect Transistors

The ultrathin body of monolayer (and few-layer) semiconducting transition-metal-dichalcogenides (TMDs) in conjunction with their highly desirable surface properties makes them excellent candidates for the ultimate downscaling of digital electronics. We have fabricated field effect transistors (FETs) of mechanically exfoliated few-atomic- layer-thick MoSe$_{2}$, a member of the semiconducting TMD family; and measured their device characteristics as a function of temperature. We find that the field-effect mobility of the devices increases with the applied back-gate voltage, which can be attributed to the Schottky barrier reduction via band bending at the contacts. In the limit of high back-gate voltages, the mobility increases from $\sim$ 135 cm$^{2}$/V.s at room temperature to over 300 cm$^{\mathrm{2}}$/V.s at 200 K following the power law of $\mu $ $\sim$ T$^{-2.1}$, indicating that the mobility is chiefly limited by phonon scattering rather than charged impurity scattering. We attribute the high mobility and its temperature dependence to the extremely low density of defects and/or impurities in the starting MoSe$_{2}$ crystals as verified by low temperature scanning tunneling microscopy/spectroscopy (STM/STS) measurements.