▎ 摘　　要

We reveal the key epitaxial growth mechanisms of single-crystalline GaN on single-crystalline graphene. We demonstrate that an AlN nucleation layer is significantly important. On the one hand, the AlN nucleation layer provides the c-axis oriented driving force for the epitaxy of GaN on graphene along the out-of-plane orientation. On the other hand, AlN islands on the dangling bonds of graphene uniformly follow the in-plane orientation of single-crystalline graphene. Moreover, the nucleation density of AlN can be increased by adjusting the pretreatment conditions of graphene. The insight gained from this work may be applied to the epitaxy of other materials on the diverse two-dimensional materials.