▎ 摘　　要

We present a theoretical study of the ballistic performance of gate-all-around field-effect transistors (FETs) with channels consisting of armchair-edge graphene nanoribbons (aGNRs) of various widths and silicon nanowires (SiNWs) with square cross sections. We apply an atomistic quantum transport formalism based on empirical pseudopotentials. Our results show that the turn-OFF behavior of aGNRFETs is seriously affected by source-to-drain tunneling at short channel lengths (e.g., below 10 nm for 3-aGNRs). Defining the threshold voltage Vth as the gate bias at which the current reaches a given I-OFF = 0.4 mu A/mu m, devices with a 5-nm channel length can reach a maximum current of only 400 mu A/mu m at a gate overdrive V-GS-V-th = 0.25 V (corresponding to an assumed V-DD of about 0.4 V). In contrast, SiNWFETs remain immune from source-to-drain tunneling even at 5 nm and show an almost ideal subthreshold swing, a satisfactory current of 1000 mu A/mu m at the same gate overdrive of 0.25 V, and a reasonable I-ON/I-OFF ratio around 2 x 10(3).