Ab initiosimulation of single- and few-layerMoS2transistors: Effect of electron-phonon scattering

Abstract

In this paper, we present full-band atomistic quantum transport simulations of single- and few-layer ${\mathrm{MoS}}_{2}$ 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-layer ${\mathrm{MoS}}_{2}$ device. With a single-gate configuration, the double-layer ${\mathrm{MoS}}_{2}$ FET shows the best intrinsic performance with an ON current, ${I}_{\text{ON}}=685\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{A}/\ensuremath{\mu}\mathrm{m}$, but with a double-gate contact the transistor with a triple-layer channel delivers the highest current with ${I}_{\text{ON}}=1850\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{A}/\ensuremath{\mu}\mathrm{m}$. The charge in the channel is almost independent of the number of ${\mathrm{MoS}}_{2}$ 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 ${MX}_{2}$ FETs because of the artificial negative differential resistance it predicts.