Atomistic Design of High Thermoelectricity on Si/Ge Superlattice Nanowires

We present predictions of thermoelectric figure of merit (ZT) on Si/Ge superlattice nanowires (SLNWs) based on ab initio electronic structure calculations and Boltzmann transport theory. Our results suggest that Si/Ge SLNW is a promising candidate for thermoelectric applications, much better than the known Si nanowires. We find that a ZT value higher than 1 at 300 K is achievable for 1.7 run diameter Si/Ge SLNW in case of a 3-order reduction on lattice thermal conductivity with respect to bulk Si. The high thermoelectric performance in Si/Ge SLNWs can be further improved by tailoring the electrical transport (S-2 sigma), which strongly depends on their unique electronic structures. We also discuss how the structural properties such as nanowire diameter, superlattice period, constituent length ratio, and the chemical potential (or doping levels) can be tuned to derive an optimal ZT for Si/Ge SLNWs.