Prediction of high zT in thermoelectric silicon nanowires with axial germanium heterostructures

TL;DR

This study predicts that axial germanium heterostructures in silicon nanowires significantly enhance thermoelectric efficiency by reducing lattice thermal conductivity, achieving high zT values even with structural disorder.

Contribution

It demonstrates that axial Ge heterostructures in silicon nanowires can greatly increase zT, providing a promising approach for high-performance thermoelectric materials.

Findings

zT reaches 3 in <111> nanowires with Ge heterostructures

Heterostructuring reduces lattice thermal conductivity substantially

High zT persists despite structural disorder

Abstract

We calculate the thermoelectric figure of merit, zT=S^2GT/(\kappa_l+\kappa_e), for p-type Si nanowires with axial Ge heterostructures using a combination of first-principles density-functional theory, interatomic potentials, and Landauer-Buttiker transport theory. We consider nanowires with up to 8400 atoms and twelve Ge axial heterostructures along their length. We find that introducing heterostructures always reduces S^2G, and that our calculated increases in zT are predominantly driven by associated decreases in \kappa_l. Of the systems considered, <111> nanowires with a regular distribution of Ge heterostructures have the highest figure-of-merit: zT=3, an order of magnitude larger than the equivalent pristine nanowire. Even in the presence of realistic structural disorder, in the form of small variations in length of the heterostructures, zT remains several times larger than that of the pristine case, suggesting that axial heterostructuring is a promising route to high-zT thermoelectric nanowires.