Electronic and Optical Properties of V_BC_B Defect in Wurtzite Boron Nitride as Potential Single-Photon Emitter: An Ab Initio Study

Single photon emitters (SPEs) are building blocks for quantum communication technologies. SPEs that emit in the near-infrared range (NIR) with a sharp zero-phonon line are optimal for this purpose. Local defects in wide band gap semiconductors can yield electronic states within the band gap (defect states) within a range allowing excitations from ~0.8 to ~1 eV. Among the materials suitable for SPEs, the allotrope of boron nitride, bulk wurtzite boron nitride (wBN), is selected for this work. The defects considered in this work consisted of a B vacancy and a carbon dopant substituting one of the two nearest B atoms to the vacancy (two configurations of the V_BC_B defect). We confirmed the thermodynamic and dynamic stability of the defects by calculating the formation energies and phonon spectra using density functional theory. To obtain the independent quasiparticle density of states as well as spin densities, the linear response GW method within the random phase approximation was utilized. To obtain the oscillator strength of the optical transitions between defect states, the Bethe-Salpeter equation method was used. The frequency-dependent dielectric function was utilized to determine the absorption spectrum. The V_BC_B defects specified in this work prove as promising NIR SPEs.