Electronic structure and thermoelectric properties of n- and p-type SnSe from first principles calculations

TL;DR

This study uses first-principles calculations to analyze the electronic structure and thermoelectric properties of n- and p-type SnSe, revealing anisotropic transport behavior and potential for high thermoelectric efficiency, especially in n-type SnSe.

Contribution

The paper provides a comprehensive first-principles analysis of SnSe's electronic and thermoelectric properties, including effects of temperature and phase transition, highlighting the superior thermoelectric potential of n-type SnSe.

Findings

SnSe exhibits strong anisotropy in electron transport properties.

p-type SnSe has non-parabolic, pudding-mold-like valence band dispersion.

n-type SnSe potentially outperforms p-type in thermoelectric efficiency.

Abstract

We present results of electronic band structure, Fermi surface and electron transport properties calculations in orthorhombic $n$- and $p$-type SnSe, applying Korringa-Kohn-Rostoker method and Boltzmann transport approach. The analysis accounted for temperature effect on crystallographic parameters in $Pnma$ structure as well as the phase transition to $CmCm$ structure at $T_c\sim 807 $K. Remarkable modifications of conduction and valence bands were notified upon varying crystallographic parameters within the structure before $T_c$, while the phase transition mostly leads to jump in the band gap value. The diagonal components of kinetic parameter tensors (velocity, effective mass) and resulting transport quantity tensors (electrical conductivity $\sigma$, thermopower $S$ and power factor PF) were computed in wide range of temperature ($15-900 $K) and, hole ($p-$type) and electron ($n-$type) concentration ($10^{17}-10^{21}$ cm$^{-3}$). SnSe is shown to have strong anisotropy of the electron transport properties for both types of charge conductivity, as expected for the layered structure. In general, $p$-type effective masses are larger than $n$-type ones. Interestingly, $p$-type SnSe has strongly non-parabolic dispersion relations, with the 'pudding-mold'-like shape of the highest valence band. The analysis of $\sigma$, $S$ and PF tensors indicates, that the inter-layer electron transport is beneficial for thermoelectric performance in $n$-type SnSe, while this direction is blocked in $p$-type SnSe, where in-plane transport is preferred. Our results predict, that $n$-type SnSe is potentially even better thermoelectric material than $p$-type one. Theoretical results are compared with single crystal $p$-SnSe measurements, and good agreement is found.