Thermoelectric Properties of Scaled Silicon Nanowires Using the sp 3 d 5 s*-SO Atomistic Tight-Binding Model and Boltzmann Transport
As a result of suppressed phonon conduction, large improvements of the thermoelectric figure of merit, ZT, have been recently reported for nanostructures compared with the raw materials' ZT values. It has also been suggested that low dimensionality can improve a device's power factor as well, offering a further enhancement. In this work the atomistic sp 3 d 5 s*-spin-orbit-coupled tight-binding model is used to calculate the electronic structure of silicon nanowires (NWs). Linearized Boltzmann transport theory is applied, including all relevant scattering mechanisms, to calculate the electrical conductivity, the Seebeck coefficient, and the thermoelectric power factor. We examine n-type NWs of diameter 3 nm and 12 nm, in , , and  transport orientations, at different carrier concentrations. Using experimental values for the lattice thermal conductivity in NWs, the expected ZT value is computed. We find that, at room temperature, although scaling the diameter below 7 nm can be beneficial to the power factor due to band structure changes alone, at those dimensions enhanced phonon and surface roughness scattering (SRS) degrade the conductivity and reduce the power factor.