Large Thermoelectric Power Factor in P-type Si (110)/[110] Ultra-Thin-Layers Compared to Differently Oriented Channels

Using atomistic electronic structure calculations and Boltzmann semi-classical transport we compute the thermoelectric power factor of ultra-thin-body p-type Si layers of thicknesses from W=3nm up to 10nm. We show that the power factor for channels in [110] transport orientation and strong (110) surface confinement largely outperforms all differently oriented channels by more than 2X. Furthermore, the power factor in this channel increases by ~40% with layer thickness reduction. This increase, together with the large confinement effective mass of the (110) surface, make this particular channel less affected by the detrimental effects of enhanced surface roughness scattering and distortion at the nanoscale. Our results, therefore, point towards the optimal geometrical features regarding orientation and length scale for power factor improvement in 2D thin-layers of zincblende semiconductors.