Exotic impurity-induced states in single-layer h -BN: The role of sublattice structure and intervalley interactions

Abstract

By using a combination of density functional theory, tight-binding, and effective mass calculations, we explore the electronic properties of donor and acceptor states of substitutional impurities in single-layer $h$-BN. We find that the impurity level structure inside the electronic gap is quite exotic, as it strongly depends on the sublattice position of the impurity and its behavior as a donor or an acceptor. For instance, when an acceptor atom replaces a nitrogen atom, the intervalley interaction induced by the impurity potential is found to be strong and the resulting level structure consists only of nondegenerate levels with strong valley and spin splitting. On the other hand, when an acceptor replaces a boron atom, the intervalley interaction is much weaker and near-valley-degenerate levels are found. Donor impurities behave in a similar fashion. The differences between these two types of level structures can be traced to the peculiar sublattice-resolved electronic structure of pristine $h$-BN, in which the valence and conduction wave functions at the $K$ and ${K}^{\ensuremath{'}}$ points are composed only of nitrogen and boron ${p}_{z}$ orbitals, respectively, and to the dependence of the intervalley interaction on them. We predict that this impurity level structure must also be present in other two-dimensional semiconductors and insulators with similar sublattice-resolved electronic states, such as other hexagonal III-V binary compounds and, consequently, offer the possibility of engineering the optical properties of these materials for potential applications in future devices.