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

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.

Site-Specific Fabrication of Blue Quantum Emitters in Hexagonal Boron Nitride

“…The high-energy peak at 216 nm is the near-band-gap emission of hBN, and the starred peak at 432 nm is the corresponding second-order peak. The next prominent feature in the spectra is a strong, narrow mid-near UV emission at 305 nm (4.1 eV); the ZPL of a well-documented defect ,,, that has been ascribed to carbon dimers in the literature, − and associated TO phonon replicas at 320 nm (3.9 eV) and 334 nm (3.7 eV). A third, less intense phonon replica is seen as a shoulder at 351 nm (3.5 eV).…”

“…For the first time, we show highly controlled, dose-dependent engineering of emitters and correlate the efficacy of the method with a spectral signature of hBN flakes. Employing nanoscale cathodoluminescence (CL) spectroscopy, we show that the effectiveness of the blue emitter generation process correlates with a well-studied carbon-related UV center at 305 nm (4.1 eV). ,,− We attribute blue emitter formation to the decomposition of carbon clusters in hBN by electron impact and show that the efficacy of the emitter fabrication method can be improved by an annealing treatment. Our findings provide a facile approach for the site-specific fabrication of quantum emitters in hBN with nanoscale resolution.…”

Universal polarization energies for defects in monolayer, surface, and bulk hexagonal boron nitride: A finite-size fragments GW approach

“…the notation CC@BN86 for a CC defect at the center of a BN86 flake or cluster. The carbon-dimer defect has been proposed [29,36] to be a likely candidate for the frequently observed 4.1 eV emission line, while the C B V N defect has been associated with the ∼2 eV emission line [33,95]. The CC-√ 7 carbon-dimer defect, with carbon atoms in 4-th nearest neighbor position, is less stable than the standard (nearest-neighbor) CC carbon-dimer defect [93].…”

“…In a previous study [36], the monolayer CC dimer defect was studied using the GW and Bethe-Salpeter formalisms within a finite-size cluster approach, following the variation of the quasiparticle gap and optical excitation energies as a function of cluster size. It was shown in particular that the defect electronic energy levels converge very slowly with system size following a 1/R 2 scaling law, with R the average radius of the defected h-BN cluster considered.…”

“…In the bulk limit, the necessity to include a sufficient number of pristine layers in the c-axis direction further increases computational cost. As a matter of fact, GW calculations for defects in h-BN were conducted essentially for monolayers [14,16,17,25,31,36,38], with one study of defected 3-layer systems [25] and one bulk study with 2-layers per unit-cell [37].…”