Photoluminescent properties of the carbon-dimer defect in hexagonal boron-nitride: a many-body finite-size cluster approach

TL;DR

This study uses many-body perturbation theories to analyze the optical and electronic properties of the carbon dimer defect in hexagonal boron-nitride, providing insights into its luminescence and excitonic characteristics.

Contribution

It introduces a finite size cluster approach with GW and Bethe-Salpeter theories to accurately predict defect properties and excitonic effects in h-BN monolayers.

Findings

Luminescence zero-phonon energy of 4.36 eV including vibrational effects

Defect HOMO-LUMO gap extrapolated to 7.6 eV in the infinite monolayer limit

Large excitonic binding energy of 3 eV for the localized exciton

Abstract

We study the carbon dimer defect in a hexagonal boron-nitride monolayer using the GW and Bethe-Salpeter many-body perturbation theories within a finite size cluster approach. While quasiparticle energies converge very slowly with system size due to missing long-range polarization effects, optical excitations converge much faster, with a $1/R^3$ scaling law with respect to cluster average radius. We obtain a luminescence zero-phonon energy of 4.36 eV, including significant 0.13 eV zero-point vibrational energy and 0.15 eV reorganization energy contributions. Inter-layer screening decreases further the emission energy by about 0.3 eV. These results bring support to the recent identification of the substitutional carbon dimer as the likely source of the zero-phonon 4.1 eV luminescence line. Finally, the GW quasiparticle energies are extrapolated to the infinite h-BN monolayer limit, leading to a predicted defect HOMO-LUMO photoemission gap of 7.6 eV. Comparison with the optical gap yields a very large excitonic binding energy of 3 eV for the associated localized Frenkel exciton.