First-principles study of the effects of electron-phonon coupling on the thermoelectric properties: a case study of SiGe compound

TL;DR

This study uses first-principles calculations to investigate how electron-phonon coupling influences thermoelectric properties in SiGe, revealing significant effects on lattice thermal conductivity and thermoelectric efficiency at high carrier concentrations.

Contribution

It provides a detailed first-principles analysis of electron-phonon interactions affecting thermoelectric performance, improving upon simplified models.

Findings

Carrier relaxation time is relatively unaffected by concentration.

Lattice thermal conductivity decreases significantly with higher carrier concentration due to electron-phonon coupling.

Thermoelectric figure-of-merit is enhanced at optimal doping and higher temperatures.

Abstract

It is generally assumed in the thermoelectric community that the lattice thermal conductivity of a given material is independent of the electronic properties. This perspective is however questionable since the electron-phonon coupling could have certain effects on both the carrier and phonon transport, which in turn will affect the thermoelectric properties. Using SiGe compound as a prototypical example, we give an accurate prediction of the carrier relaxation time by considering scattering from all the phonon modes, as opposed to the simple deformation potential theory. It is found that the carrier relaxation time does not change much with the concentration, which is however not the case for the phonon transport where the lattice thermal conductivity can be significantly reduced by electron-phonon coupling at higher carrier concentration. As a consequence, the figure-of-merit of SiGe compound is obviously enhanced at optimized carrier concentration, and becomes more pronounced at elevated temperature.