Electron- and phonon transport in silicon nanowires: an atomistic approach to thermoelectric properties

TL;DR

This study uses an atomistic approach to analyze electron and phonon transport in disordered silicon nanowires, revealing how surface vacancies influence thermoelectric efficiency and identifying conditions for high ZT values.

Contribution

It introduces a method to accurately estimate average transmissions in disordered nanowires using vacancy scattering properties, advancing thermoelectric material modeling.

Findings

Phonon transmission is more affected by vacancies than electronic transmission.

Disordered <111> oriented wires with 2 nm diameter achieve ZT > 3.

Surface vacancies can enhance thermoelectric performance.

Abstract

We compute both electron- and phonon transmissions in thin disordered silicon nanowires. Our atomistic approach is based on tight-binding and empirical potential descriptions of the electronic and phononic systems, respectively. Surface disorder is modeled by including surface silicon vacancies. It is shown that the average phonon- and electron transmissions through long SiNWs containing many vacancies can be accurately estimated from the scattering properties of the isolated vacancies using a recently proposed averaging method [Phys. Rev. Lett. 99, 076803 (2007)]. We apply this averaging method to surface disordered SiNWs in the diameter range 1-3 nm to compute the thermoelectric figure of merit, ZT. It is found that the phonon transmission is affected more by the vacancies than the electronic transmission leading to an increased thermoelectric performance of disordered wires, in qualitative agreement with recent experiments. The largest ZT>3 is found in strongly disordered <111> oriented wires with a diameter of 2 nm.