Electronic and Optical Properties of Two-Dimensional α-PbO from First Principles

We performed first-principles calculations based on density functional theory and many-body perturbation theory to investigate the electronic and optical properties of monolayer, bilayer, and bulk litharge α-PbO, including spin–orbit coupling effects. The fundamental gap is direct for the monolayer (4.48 eV) and indirect for the bilayer (3.44 eV) and the bulk material (2.45 eV). The exciton binding energies are large for the monolayer (1.1 eV) and the bilayer (0.9 eV), indicating that excitons are stable at room temperature. However, the lowest-energy excitons for the monolayer and the bilayer are dark with radiative lifetimes on the order of milliseconds. A pronounced van Hove singularity in the valence band of the few-layer structures suggests it becomes a multiferroic two-dimensional material upon hole doping. Our results indicate strong optical absorbance in the vacuum UV region and transparency in the visible and near UV for monolayer PbO, suggesting applications for atomically thin solar-blind UV photodetectors.