Study on Nucleation and Growth Mode of GaN on Patterned Graphene by Epitaxial Lateral Overgrowth

Thereare two types of GaN nucleation on graphene masks,where nucleation at the steps on the sides of the window is beneficialto reduce the dislocation density of the epilayer. During the earlystage of growth, the graphene mask can be observed using HRTEM, butit gradually disappears as the growth continues due to the effectof substrate decomposition. Inthe past two decades, using dielectric materials such as SiO2 as a mask for the lateral epitaxial growth of gallium nitride(GaN) has matured, but the properties of films using amorphous maskmaterials are already difficult to improve, which limits the applicationof GaN. In this study, the quality of GaN films was enhanced by epitaxiallateral overgrowth (ELOG) on graphene mask/GaN template by metal-organicchemical vapor deposition. We found two types of nucleation and growthmode of GaN on the compound substrate and that graphene was slowlyand continuously destroyed during growth. Using scanning transmissionelectron microscopy and Raman spectroscopy to analyze graphene betweenthe GaN epilayer and the substrate at various periods of growth, theresults showed that graphene was stable and had a distinct layer structureat the initial stage of growth, and as the growth processed, the graphenemasks were disrupted due to the decomposition of the GaN substrate,and eventually air gaps of approximately 240 nm appeared at the positionsof graphene masks. Although graphene is gradually decomposed, graphenemasks still effectively block the dislocation from extending intothe epilayer in the process, and GaN still maintains the trend ofELOG. The dislocation density of the GaN film is decreased to 1-3x 10(7) cm(-2), which can be estimatedvisually by cathodoluminescence. This feature of graphene providesa valuable strategy for the future research of large-area self-standingGaN films on GaN templates.