Single-photon emitters in hexagonal boron nitride: a review of progress

Abstract

This report summarizes progress made in understanding properties such as zerophonon-line energies, emission and absorption polarizations, electron-phonon couplings, strain tuning and hyperfine coupling of single photon emitters in hexagonal boron nitride. The primary aims of this research are to discover the chemical nature of the emitting centres and to facilitate deployment in device applications. Critical analyses of the experimental literature and data interpretation, as well as theoretical approaches used to predict properties, are made. In particular, computational and theoretical limitations and challenges are discussed, with a range of suggestions made to overcome these limitations, striving to achieve realistic predictions concerning the nature of emitting centers. A symbiotic relationship is required in which calculations focus on properties that can easily be measured, whilst experiments deliver results in a form facilitating mass-produced calculations.

Edge effects on optically detected magnetic resonance of vacancy defects in hexagonal boron nitride

“…Table 2 lists critical calculated properties of the triplet manifold for defects located in the bulk and at the considered edge. These include the adiabatic transition energies ΔE 0 , likely to be a good approximation for observed ZPL energies ΔE 00 ; vertical excitation energies ΔE A v , and the absorption and emission reorganisation energies λ A and λ E , respectively, that depict spectral bandwidths 13 . a b State symmetry for bulk defects is expressed in terms of both D 3h to C 2v symmetry 43 , with spontaneous symmetry lowering mandated by Jahn-Teller distortion for doubly degenerate states; all edge defects intrinsically have C 2v symmetry; V À N in the centre (bulk) is also unstable owing to warping of the plane to C 2 symmetry.…”

“…Their exploitation, however, requires understanding of the chemical nature of the colour centres in h-BN and the ability to control and tune their structural arrangements and spectroscopic properties. Whilst various colour centres have been proposed and examined computationally as potential sources of SPEs in h-BN [9][10][11][12][13][14][15] , none have been firmly identified 13 . In parallel to this work, defect centres in h-BN have also been demonstrated to produce strong paramagnetic effects, and for these chemical assignments have indeed been developed 13 .…”

“…The most commonly applied computational approach to predicting the optical and magnetic properties of defects is densityfunctional theory (DFT) 13 . The prediction of optical spectroscopic properties, such as the zero phonon line (ZPL) energy, by DFT is very difficult as most defect states are open-shell in nature, displaying multi-reference characteristics, whereas DFT is intrinsically a single-reference approach 24 .…”

“…The prediction of optical spectroscopic properties, such as the zero phonon line (ZPL) energy, by DFT is very difficult as most defect states are open-shell in nature, displaying multi-reference characteristics, whereas DFT is intrinsically a single-reference approach 24 . Time-dependent DFT (TDDFT) can be reliable for defect excited states, provided that it is performed based on a well-represented reference state, as indeed is the case for the triplet manifold of V À B 13 . Nevertheless, DFT is typically quite accurate when it comes to the prediction of ground-state magnetic properties 13 , for example using the Heyd-Scuseria-Ernzerhof hybrid functional (HSE06) 25,26 .…”

“…Time-dependent DFT (TDDFT) can be reliable for defect excited states, provided that it is performed based on a well-represented reference state, as indeed is the case for the triplet manifold of V À B 13 . Nevertheless, DFT is typically quite accurate when it comes to the prediction of ground-state magnetic properties 13 , for example using the Heyd-Scuseria-Ernzerhof hybrid functional (HSE06) 25,26 . Indeed, DFT predictions of the hfc and ZFS properties of the nitrogen vacancy (NV) centre in diamond 27,28 were important for the identification of its chemical structure.…”