  An optical phonon limited velocity model has been employed to investigate
high-field transport in a selection of layered 2D materials for both, low-power
logic switches with scaled supply voltages, and high-power, high-frequency
transistors. Drain currents, effective electron velocities and intrinsic
cut-off frequencies as a function of carrier density have been predicted thus
providing a benchmark for the optical phonon limited high-field performance
limits of these materials. The optical phonon limited carrier velocities of a
selection of transition metal dichalcogenides and black phosphorus are found to
be modest as compared to their n-channel silicon counterparts, questioning the
utility of these devices in the source-injection dominated regime. h-BN, at the
other end of the spectrum, is shown to be a very promising material for
high-frequency high-power devices, subject to experimental realization of high
carrier densities, primarily due to its large optical phonon energy.
Experimentally extracted saturation velocities from few-layer MoS2 devices show
reasonable qualitative and quantitative agreement with predicted values.
Temperature dependence of measured vsat is discussed and found to fit a
velocity saturation model with a single material dependent fit parameter.
