Atomistic Modeling of the Thermoelectric Properties in Silicon Nanowires

The thermoelectric properties of Silicon can be improved due to nano-sized structuring and modulation. The effect of crystal orientation, cross-sectional dimension and source-drain doping on Seebeck coefficient (S) and electronic conductance ($\sigma$) in silicon nanowires is studied theoretically in this work. From the electronic structure obtained using an atomistic 10 band $sp^{3}d^{5}s^{*}$ Tight-Binding model with spin orbit coupling, we calculate these parameters using the Landauer formula. Conductivity increases with increasing cross-section size since the number of modes per energy increases. Different orientations show different conductivity. However, Seebeck coefficient is quite independant of the orientation and cross-section size. But, the power factor ($S^{2}\sigma$), can be improved with size and orientation mainly due to the improvement in conductivity. In these nanowires, phonon scattering at the wire boundary further reduces the lattice thermal conductivity ($\kappa_{l}$) which plays a positive role in improving the thermoelectric figure of merit (ZT) bringing it close to 1 at 300K.