Phonon-assisted optical absorption in BaSnO$_3$ from first principles

TL;DR

This study uses first-principles calculations to show that electron-phonon interactions and hybrid functional exchange are crucial for accurately modeling phonon-assisted optical absorption in BaSnO$_3$, impacting transparent conductor design.

Contribution

It provides a detailed first-principles analysis highlighting the importance of electron-phonon interactions and electronic correlations in BaSnO$_3$'s optical properties.

Findings

Electron-phonon interactions enable phonon-assisted absorption across the indirect gap.

Temperature influences the optical absorption spectrum.

Electronic correlations are essential for structural stability and accurate band energies.

Abstract

The perovskite BaSnO$_3$ provides a promising platform for the realization of an earth abundant $n$-type transparent conductor. Its optical properties are dominated by a dispersive conduction band of Sn $5s$ states, and by a flatter valence band of O $2p$ states, with an overall indirect gap of about $2.9$ eV. Using first-principles methods, we study the optical properties of BaSnO$_3$ and show that both electron-phonon interactions and exact exchange, included using a hybrid functional, are necessary to obtain a qualitatively correct description of optical absorption in this material. In particular, the electron-phonon interaction drives phonon-assisted optical absorption across the minimum indirect gap and therefore determines the absorption onset, and it also leads to the temperature dependence of the absorption spectrum. Electronic correlations beyond semilocal density functional theory are key to detemine the dynamical stability of the cubic perovskite structure, as well as the correct energies of the conduction bands that dominate absorption. Our work demonstrates that phonon-mediated absorption processes should be included in the design of novel transparent conductor materials.