Point charged defects in 2D and 3D h-BN: A density functional theory study

In this work, we first calibrated a density functional theory (DFT) approach, and then I carried out DFT calculations to study the properties of charged point defects in monolayer, bilayer, and bulk h-BN. In particular, we considered a DFT approach using a semiempirical scheme to account for Van der Waals forces, and we optimized the dispersive coefficient of B to obtain a description of the structural and mechanical properties of bulk h-BN in agreement with the experiments. The resulting optimized DFT scheme was used to calculate formation energies and electronic properties of neutral and charged B and N vacancies, as well as C substitutional defects for both N and B sites. To correct the formation energies of charged defects, we used a novel polarizable force field. Our calculations show that, due to electrostatic polarization, the formation energy of charged defects in bilayer h-BN is about 0.5 eV lower than in monolayer h-BN. Furthermore, we found that assuming that the aforementioned four types of point defects are present with a finite concentration in mono- and bi-layer h-BN, there is always a class of defects that is likely to be charged, regardless of the position of the Fermi level.