First-Principles Study on the Defect-Induced characteristics in Hexagonal Boron Nitride

Atomic defects in hexagonal boron nitride (hBN) have attracted much interest, not only because they are much easier to manipulate, but also because they give rise to intriguing phenomena not observed in its perfect counterpart. For example, many previous studies have reported luminescence due to the defects inducing the mid-gap states. Other studies have reported their spin characteristics, which appear when the defects break their equilibrium magnetic configurations and respond to the external magnetic fields. One of the most challenging parts of exploiting these defects is the accurate identification of the atomic defect structures, since experiments usually observe the collective features of crystals, not the specific atomic configurations or their local phenomena, although they clearly affect physical properties such as the energy spectrum of photoemission or spin configurations. Therefore, we performed first-principles calculations using density functional theory to unambiguously study different types of atomic vacancies in the hBN. The stabilities of these defects were determined by evaluating their formation energies, which are well defined from a thermodynamic point of view. Then, we explored the defect states, comparing our results with the previous experiments, in order to provide clues to identify the origin of some exotic features, such as photoluminescence in the different energy ranges or the appearance of the magnetic moments. We also investigated the defect configurations in hBN in the presence of other 2D layers forming bilayer heterostructures to present in detail the substrate effects on their geometric and electronic structures.