Symmetry-dependent band gap opening in graphene induced by g-C₃N₄ substrates

Opening the band gap in graphene can significantly broaden its applications in electronic devices. By introducing four types of graphene-like carbon nitride (g-C₃N₄) as the substrate of graphene, we reveal, with first principles calculations, a symmetry and size dependent band gap opening in graphene. On the one hand, for a substrate with a 3-fold rotational symmetry, a small C₃N₄ unit can cause a large value of the band gap in the graphene layer. On the other hand, the band gap also depends on the symmetry of the substrate. A 3-fold symmetry induces a relatively small band gap, while rectangular and oblique symmetries result in a relatively large band gap opening in graphene but cause a much heavier effective mass of charge carriers. The former case is due to the nonequivalence of sub-lattices in graphene induced by the substrate, while for the latter case, interfacial hybridization plays the main role in band gap opening in graphene. Our theoretical findings could pave the way for the use of graphene-based semiconductor devices.