Photoemission Study of the Electronic Structure of Valence Band Convergent SnSe

TL;DR

This study uses angle-resolved photoemission spectroscopy to experimentally determine the electronic band structure of SnSe, confirming theoretical predictions and elucidating the electronic factors behind its high thermoelectric efficiency.

Contribution

First direct experimental observation of the multiple valence bands in SnSe, validating theoretical models and clarifying the electronic structure related to thermoelectric performance.

Findings

Three hole bands observed with small energy differences

Good agreement with ab initio calculations

Insights into electronic origins of thermoelectric efficiency

Abstract

IV-VI semiconductor SnSe has been known as the material with record high thermoelectric performance.The multiple close-to-degenerate valence bands in the electronic band structure has been one of the key factors contributing to the high power factor and thus figure of merit in the SnSe single crystal. To date, there have been primarily theoretical calculations of this particular electronic band structure. In this paper, however, using angle-resolved photoemission spectroscopy, we perform a systematic investigation of the electronic structure of SnSe. We directly observe three predicted hole bands with small energy differences between their band tops and relatively small in-plane effective masses, in good agreement with the ab initio calculations and critical for the enhancement of the Seebeck coefficient while keeping high electrical conductivity. Our results reveal the complete band structure of SnSe and help to provide a deeper understanding of the electronic origin of the excellent thermoelectric performances in SnSe.