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

In the 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 mask materials are already difficult to improve, which limits the application of GaN. In this study, the quality of GaN films was enhanced by epitaxial lateral overgrowth (ELOG) on graphene mask/GaN template by metal–organic chemical vapor deposition. We found two types of nucleation and growth mode of GaN on the compound substrate and that graphene was slowly and continuously destroyed during growth. Using scanning transmission electron microscopy and Raman spectroscopy to analyze graphene between the GaN epilayer and the substrate at various periods of growth, the results showed that graphene was stable and had a distinct layer structure at the initial stage of growth, and as the growth processed, the graphene masks were disrupted due to the decomposition of the GaN substrate, and eventually air gaps of approximately 240 nm appeared at the positions of graphene masks. Although graphene is gradually decomposed, graphene masks still effectively block the dislocation from extending into the epilayer in the process, and GaN still maintains the trend of ELOG. The dislocation density of the GaN film is decreased to 1–3 × 107 cm–2, which can be estimated visually by cathodoluminescence. This feature of graphene provides a valuable strategy for the future research of large-area self-standing GaN films on GaN templates.