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

The Thomas Young Centre for Theory and Simulation of Materials, Imperial College London London SW7 2AZ, UK

^a a.mostofi@imperial.ac.uk

Received: 11 March 2011
Accepted: 5 May 2011

Abstract

We calculate the thermoelectric figure of merit, zT=S²GT/(κ_l+κ_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 S²G, and that our calculated increases in zT are predominantly driven by associated decreases in κ_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.