Energetics and electronic structures of thin films and heterostructures of a hexagonal GaN sheet

Abstract

Using the density functional theory (DFT) combined with van der Waals correction and effective screening medium methods, we study the geometric and electronic structures of GaN thin films, each atomic layer of which exhibits a hexagonally bonded two-dimensional (2D) network. Our DFT calculations containing the van der Walls correction showed that the hexagonal GaN (h-GaN) sheets in the thin films are tightly bound to each other owing to the small interlayer spacing, such that their electronic structures are sensitive to the number of layers. We also investigate the energetics and electronic structures of hybrid structures of h-GaN with other layered materials, graphene and h-BN: For both hybrids, the optimum interlayer spacing is 3.4 Å, indicating that the h-GaN sheet is bound to graphene or h-BN via a weak van der Waal interaction. Owing to the weak interlayer interaction, graphene and h-BN retain their characteristic electronic structures. We further found that GaN thin films with a wurtzite structure undergo a structural phase transition into the layered structure of h-GaN when a biaxial tensile strain is applied.