Large enhancement in hole velocity and mobility in p-type [110] and [111] silicon nanowires by cross section scaling: An atomistic analysis

The mobility of p-type nanowires (NWs) of diameters of D=12nm down to D=3nm, in [100], [110], and [111] transport orientations is calculated. An atomistic tight-binding model is used to calculate the NW electronic structure. Linearized Boltzmann transport theory is applied, including phonon and surface roughness scattering (SRS) mechanisms, for the mobility calculation. We find that large mobility enhancements (of the order of 4X) can be achieved as the diameter of the [110] and even more that of the [111] NWs scales down to D=3nm. This enhancement originates from the increase in the dispersion curvatures and consequently the hole velocities as the diameter is scaled. This benefit over compensates the mobility reduction caused by SRS as the diameter reduces. The mobility of the [100] NWs, on the other hand, is the lowest compared the other two NW orientations, and additionally suffers as the diameter scales. The bandstructure engineering techniques we describe are a generic feature of anisotropic bulk bands, and can be also applied to 2D thin-body-layers as well as other channel materials.