Optical properties of single-crystal As2Se3 from first principles

Abstract

Crystalline As2Se3 is a promising layered chalcogenide for mid-infrared photonics and optoelectronic applications, yet its fundamental electronic and optical properties remain debated. This paper combines density functional theory with G0W0 quasiparticle corrections and Bethe-Salpeter equation (BSE) calculations to deliver a robust description of its band structure and optical response. The G0W0 results reveal an indirect band gap of 2.31 eV with nearly degenerate direct transitions at Gamma, while the BSE spectra exhibit strong polarization-dependent anisotropy and pronounced excitonic effects. Several bound excitons are identified near the absorption onset, clarifying the role of electron-hole interactions and resolving previous controversies regarding the nature of the optical gap and the contribution of lone-pair states. This work provides a unified and quantitatively accurate picture of As2Se3, reinforcing its potential for next-generation infrared and anisotropic photonic devices.