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

We study the carbon-dimer defect in a hexagonal boron-nitride (h-BN) monolayer using the GW and BetheSalpeter 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. Interlayer 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 highest occupied molecular orbital to lowest unoccupied molecular orbital 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.

Automated summary

The study revealed a luminescence zero-phonon energy of 4.36 eV in the carbon-dimer defect in h-BN monolayer, including contributions from zero-point vibrational energy and reorganization energy. Interlayer screening further decreased the emission energy by about 0.3 eV. The comparisons with optical gaps suggested a large excitonic binding energy of 3 eV for the associated localized Frenkel exciton.