Impact of oxide thickness on the performance of a GaAs NWFET

Abstract

Nanowire field effect transistors (NWFETs) are being considered as a replacement for planar MOSFETs at the end of the ITRS. In this work, the change in the relative position of the valleys due to the oxide thickness is investigated, and the subsequent effect this has on the drain current in each valley. An NWFET of cross-section 2.2×2.2 nm2 and channel length 6 nm has been considered. The strong confinement at this scale can cause the low mass Γ-valley to become raised in energy, such that it is higher than the heavy mass L and X-valleys. This results in very low current in the device. It was found that increasing the oxide from 0.2 nm to 0.8 nm caused the Γ-valley to lower in energy, resulting in a higher current. Both ballistic and dissipative transport are considered. This was achieved through the use of the non-equilibrium Green's function (NEGF) formalism. The mode space approach in the effective mass approximation was deployed, and the conduction band masses were extracted from tight binding simulations. Scattering was found to cause a 65%, 44% and 36% in the current for a 0.2 nm, 0.8 nm and 1.6 nm oxide thickness respectively.