Strong anisotropy and diameter effects on the low-field mobility of silicon nanowires

We describe a method to couple the sp3d5s*-spin-orbit-coupled (SO) atomistic tight-binding (TB) model and linearized Boltzmann transport theory for the calculation of low-field mobility in Si nanowires (NWs). We consider scattering mechanisms due to phonons and surface roughness. We perform a simulation study of the low-field mobility in n-type and p-type Si NWs of diameters from 3nm to 12nm, in the [100], [110] and [111] transport orientations. We find that the NW mobility is a strong function of orientation and diameter. This is a consequence of the large variations in the electronic structure with geometry and quantization. Especially in the case of p-type [111] and [110] NWs, large phonon-limited mobility improvements with diameter scaling are observed.