Ab initio simulation of single- and few-layer MoS2 transistors: Effect of electron-phonon scattering

In this paper, we present full-band atomistic quantum transport simulations of single- and few-layer MoS2 field-effect transistors (FETs) including electron-phonon scattering. The Hamiltonian and the electron-phonon coupling constants are determined from ab initio density-functional-theory calculations. It is observed that the phonon-limited electron mobility is enhanced with increasing layer thicknesses and decreases at high charge concentrations. The electrostatic control is found to be crucial even for a single-layerMoS(2) device. With a single-gate configuration, the double-layer MoS2 FET shows the best intrinsic performance with an ON current, ION = 685 mu A/mu m, but with a double-gate contact the transistor with a triple-layer channel delivers the highest current with ION = 1850 mu A/mu m. The charge in the channel is almost independent of the number of MoS2 layers, but the injection velocity increases significantly with the channel thickness in the double-gate devices due to the reduced electron-phonon scattering rates in multilayer structures. We demonstrate further that the ballistic limit of transport is not suitable for the simulation of MX2 FETs because of the artificial negative differential resistance it predicts.