Native Defects of the Ultranarrow-Bandgap Semiconductor γ-SnSe and Their Effect on Its Electronic, Optical, and Thermoelectric Properties

SnSe is attractive due to its excellent thermoelectric properties and the scarcity of tellurium. Very recently, γ-SnSe, with an ultranarrow bandgap, was discovered at the nanoscale. It exhibits promising optical properties, including a wide absorption range from IR to UV, suggesting its potential to capture a significant portion of the solar spectrum as an active absorber layer. Here, we explore its electronic properties for optoelectronic and thermoelectric applications. Specifically, we investigate the native defects in γ-SnSe and their effects on its electronic, optical, and thermoelectric properties. Similar to its α-SnSe counterpart, the cation and anion vacancies were found to be the energetically most stable intrinsic defects in γ-SnSe under Se-rich and Sn-rich conditions, respectively. We found that overall defects have a minimal effect on the bandgap and the optical properties, but influence their anisotropy. Additionally, we investigated the thermoelectric properties of γ-SnSe and found the power factor to be comparable to that of its α-Pnma counterpart.