Exotic hydrogenic impurity states in h-BN: the role of the structure and intervalley interactions

In this work, we employ a combination of theoretical calculations to explore the electronic properties of donor and acceptor states of substitutional impurities in h-BN, a wide-gap 2D insulator. We find that the structure of the impurity levels that appear inside the electronic gap strongly depends on the atom replaced by the impurity. For instance, when an acceptor replaces a N atom, the intervalley interaction induced by the impurity is found to be strong and the resulting level structure consists only of non-degenerate levels with strong valley and spin splittings. On the other hand, when an acceptor replaces a B atom, the intervalley interaction is much weaker and a near-valley-degenerate ground state is found. Donor impurities behave on a similar fashion. We show that the differences between these level structures can be traced to the peculiar sublattice-resolved electronic structure of pristine h-BN. In fact, these exotic impurity levels may also be present in other 2D semiconductors and insulators with similar bandstructures, such as other hexagonal III-V compounds, and their optical properties may be engineered for applications in future optoelectronic devices.