Monolayer to bulk properties of hexagonal boron nitride

Hexagonal boron nitride (h-BN) has attracted a lot of attention as a layered material in which the layers are weakly bound by van der Waals interactions. h-BN is being explored as a host for single-photon emitters and as a dielectric in heterostructures comprised of two-dimensional materials. For these applications an accurate description of the evolution of the electronic structure of h-BN as a function of the number of layers is required. We will present hybrid functional calculations of the electronic structure of h-BN as a function of the number of layers, starting from a monolayer, which has a direct band gap. Above a monolayer the band gap becomes indirect. We find that, with respect to the vacuum level, the conduction band at M decreases as the number of layers increases which leads to the direct-to-indirect cross over. These findings are analyzed in terms of the orbital composition and effective masses at the band edges at various high-symmetry points in the Brillouin zone.