Abstract
We investigate defect properties in hexagonal boron nitride (hBN) which is attracting much attention as a single photon emitter. Using first-principles calculations, we find that nitrogen-vacancy defect V N has a lower energy structure in C 1 h symmetry in 1− charge state than the previously known D 3 h symmetry structure. Noting that carbon has one more valence electron than boron species, our finding naturally points to the correspondence between V N and V N C B defects with one charge state difference between them, which is indeed confirmed by the similarity of atomic symmetries, density of states, and excitation energies. Since V N C B is considered as a promising candidate for the source of single photon emission, our study suggests V N as another important candidate worth attention, with its simpler form without the incorporation of foreign elements into the host material.
Highlights
Besides zero-phonon line (ZPL) at around 2 eV energy, other physical properties relevant to identify the source of single photon emission (SPE) include the
After C1h symmetry with out-of-plane relaxation is confirmed as the ground state atomic configuration of the VNCB defect, we investigate the possible analogy between VNCB and VN with one more electron
In the neutral state with two electrons, both spinup and down states are occupied by an electron each, as shown in Figure 2(a), exhibiting a spin “singlet” state. e energy gain by the out-of-plane relaxation of the carbon atom is enhanced by the presence of two electrons compared with the case of only one electron in the 1+ charge state, explaining the enhanced symmetry breaking with the larger out-of-plane displacement of the carbon atom in the neutral state compared with the 1+ charge state as depicted in Figures 1(a) and 1(b). e electronic structure of VN defect has a close analogy with that of VNCB as expected, displayed in Figures 2(c) and 2(d)
Summary
We investigate the stable atomic structure of VNCB, which has been suggested as one of the promising candidates as the source of SPE. When an electron is removed to become 1+ charged state VNC1B+, it still retains C1h symmetry, but with much reduced out-of-plane displacements (0.2 Afor the carbon atom), as shown, which is closer to C2v symmetry than the neutral state. E energy gain by the out-of-plane relaxation of the carbon atom is enhanced by the presence of two electrons compared with the case of only one electron in the 1+ charge state, explaining the enhanced symmetry breaking with the larger out-of-plane displacement of the carbon atom in the neutral state compared with the 1+ charge state as depicted in Figures 1(a) and 1(b). In the case of V1N−, which has two electrons, same with VNC0B, the spin singlet configuration is obtained with the enhanced symmetry breaking out-of-plane atomic displacement, as shown in Figures 1(c) and 1(d). For VNCB, 1+/0 CTL, which corresponds the position of EF below (above) which 1+ charge (neutral) state is stabilized, is estimated to be 1.57 eV above the valence band minimum
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