Bistable carbon-vacancy defects in $h$-BN

TL;DR

This study uses density functional theory to analyze carbon-vacancy defects in hexagonal boron nitride, finding that these defects are charge-dependent and unlikely to be the source of observed single photon emitters.

Contribution

It systematically investigates two specific carbon-vacancy defect configurations and their stability, providing insights into their likelihood as single photon emitters in h-BN.

Findings

VNCB is the dominant defect based on formation energy.

CNVB can transform into VNCB in certain charge states.

Neither defect matches the observed fluorescence spectra.

Abstract

Single photon emitters in hexagonal boron nitride have been extensively studied recently. Although unambiguous identification of the emitters is still under intense research, carbon related defects are believed to play a vital role for the emitter producing zero-phonon-lines in the range of $1.6$ to $2.2$~eV. In this study, we systematically investigate two configurations of carbon-vacancy defects, VNCB and CNVB, by means of density functional theory calculations. We calculated the reaction barrier energies from one defect to the other to determine relative stability. We find the barrier energies are charge dependent and CNVB could easily transform to VNCB in neutral and positive charge states while it is stable when negatively charged. Formation energy calculations show that the VNCB is the dominant defect over CNVB. However, neither VNCB nor CNVB has suitable fluorescence spectra that could reproduce the observed ones. Our results indicate that the origin of the $1.6$-to-$2.2$-eV emitters should be other carbon-related configurations.