Novel Defect-complexes in Hexagonal Boron Nitride with Topologically Tunable Attributes for Quantum Technologies

This computational investigation reveals a new family of tunable visible-range color centers in hexagonal boron nitride (hBN) comprising of either C- and O-based with vacancy (CBONVB, CNONVB, CNOBVN) or C- and O-based with substitutional defects (CNOBBN, CNONNB). These defect configurations induce pronounced alterations in the structural stability, electronic structure and optical response of the hBN system, with the magnitude of these effects strongly dictated by the local environment near the vicinity of the defect and the nature of the substitutional defect. The defect-complexes with similar localized geometries (CNONVB, CNOBVN) exhibit nearly identical structural stability, whereas the distinct CBONVB configuration enhances the structural stability. The complex-defect type determines the position of the intragap defect states and the nature of variation of the energy bandgap. The computed absorption spectra underlines that the absorption range, spectral shifts and the entire peak profile are extremely sensitive to the local defect environment and the type of dopant occupying the specific vacancy site. The transition dipole moment density maps shows that the electron-hole confinement character decides the direction of energy shift exhibited by the brightest exciton. The replacement of vacancy by dopants reduces the charge-transfer length, signifying that vacancy-based defects are more crucial for photoluminescence application. The zero-phonon line energy can be effectively tuned by altering the local defect geometry and type of substitutional defect, offering new opportunities for defect engineered hBN in optoelectronic and quantum technologies.