Bias-Induced Hole Mobility Increase in Narrow [111] and [110] Si Nanowire Transistors

We report on the phonon-limited hole mobility of ultra-narrow Si nanowire (NW) channel transistors as a function of inversion charge density. We employ atomistic bandstructure calculations and linearized Boltzmann transport theory and examine NWs of 12 nm in diameter in [100], [110], and [111] transport orientations. We show that the curvature of the bands in the [110] and [111] NWs increases significantly as the channel is driven into inversion, which results in a ~ 50% mobility increase. In the case of the [100] NW, on the other hand, such feature is not observed.