Dominant electron-phonon scattering mechanisms in $n$-type PbTe from first principles

TL;DR

This study uses first-principles calculations to identify dominant electron-phonon scattering mechanisms in n-type PbTe, revealing that optical phonons dominate transport while soft phonons do not impair electronic mobility, explaining its high thermoelectric efficiency.

Contribution

It provides a detailed first-principles analysis of electron-phonon interactions in n-type PbTe, highlighting the role of soft phonons in thermoelectric performance.

Findings

Longitudinal optical phonon scattering dominates electronic transport.

Soft transverse optical phonons have minimal impact on mobility.

Soft phonons suppress thermal conductivity without degrading electronic transport.

Abstract

We present an \emph{ab-initio} study that identifies the main electron-phonon scattering channels in $n$-type PbTe. We develop an electronic transport model based on the Boltzmann transport equation within the transport relaxation time approximation, fully parametrized from first-principles calculations that accurately describe the dispersion of the electronic bands near the band gap. Our computed electronic mobility as a function of temperature and carrier concentration is in good agreement with experiments. We show that longitudinal optical phonon scattering dominates electronic transport in $n$-type PbTe, while acoustic phonon scattering is relatively weak. We find that scattering due to soft transverse optical phonons is by far the weakest scattering mechanism, due to the symmetry-forbidden scattering between the conduction band minima and the zone center soft modes. Soft phonons thus play the key role in the high thermoelectric figure of merit of $n$-type PbTe: they do not degrade its electronic transport properties although they strongly suppress the lattice thermal conductivity. Our results suggest that materials like PbTe with soft modes that are weakly coupled with the electronic states relevant for transport may be promising candidates for efficient thermoelectric materials.