Stable holey two-dimensional C₂N structures with tunable electronic structure

We investigate the phonon stability of several bulk C₂N holey two-dimensional crystals (C₂N-h2D), a recently synthesized carbon nitride layered material, by using first-principles calculations. Among the polytypes addressed, only one does not display phonon instabilities. The electronic structure evolution of dynamically stable C₂N-h2D from monolayer to bilayer and to bulk is unveiled. The direct band gap at Γ can be decreased by 34% from monolayer to bulk, offering opportunities in optoelectronics. The effective masses of both carriers become smaller as the number of layers increases, and their anisotropy along in-plane directions displayed in the monolayer is reduced, which suggest that the carrier mobility may be tuned as well. These effects are then explained according to the interaction of the orbitals in neighboring layers.