Structural phase transition of graphene caused by GaN epitaxy

We report first-principles predictions, where the structure of graphene changes drastically with the epitaxial growth of GaN (which has been performed experimentally). We identify GaN-3×3/graphene-2 × 2 superstructure as the most probable interface atomic structure, where three C-C bonds are replaced with C-N-C bonds preserving the Dirac cones. As the GaN epitaxy proceeds expanding graphene gradually, the tensile strain for graphene is released suddenly by partial breaking of the C-bond network, attributable to the two-dimensionality of graphene. In contrast, graphene retains its honeycomb structure at the AlN-graphene interface. Both of GaN- and AlN-graphene interfaces exhibit spin polarization.