The lattice and electronic thermal conductivity of doped SnSe: a first-principles study

TL;DR

This study uses first-principles calculations to analyze how doping affects thermal conductivity in SnSe, revealing weak electron-phonon interactions for phonons and significant electronic thermal conductivity at high doping levels.

Contribution

It provides a detailed first-principles analysis of electron and phonon contributions to thermal transport in doped SnSe, clarifying the role of charge carriers and electron-phonon coupling effects.

Findings

Electron-phonon coupling is weak compared to phonon-phonon scattering.

Electronic thermal conductivity becomes significant at carrier concentrations above 10^{19} cm^{-3}.

Lorenz number varies with orientation, doping, and carrier type.

Abstract

Recently, it has been found that crystalline tin selenide (SnSe) holds great potential as a thermoelectric material due to its ultralow thermal conductivity and moderate electronic transport performance. As thermoelectric application usually requires doped material, charge carriers can play a role in the thermal transport in doped SnSe, but such an effect has not been clearly elucidated in previous theoretical and experimental studies. Here we performed a fully first-principles study on the effects of electrons to the thermal transport in doped SnSe. The electron-phonon coupling (EPC) effects on both phonons and charge carriers were considered using the mode specific calculation in our work. It is found that for phonons, EPC are weak compared to the intrinsic phonon-phonon scattering even at high carrier concentrations and thus have negligible effects on the lattice thermal conductivity. The electronic thermal conductivity is not negligible when the carrier concentration is higher than $10^{19} cm^{-3}$ and the values can be as high as 1.55, 1.45 and 1.77 $Wm^{-1}K^{-1}$ on a, b and c axes, respectively, for $10^{20} cm^{-3}$ electron concentration at 300K. The Lorenz number of SnSe is also calculated and it is dependent on crystal orientations, carrier concentrations, and carrier types. The simple estimation of electronic thermal conductivity using Wiedemann-Franz law can cause large uncertainties for doped SnSe.