Roles of Nanoscale Defects of Graphene in Remote Epitaxy of GaN

Remote epitaxy through graphene enables the fabrication of freestanding membranes, facilitating the "peel-and-stack" process for semiconductor hetero-integration. While previous studies have emphasized graphene thickness, substrate bonding ionicity, and damage-free transfer of graphene for implementing remote epitaxy, the impact of nanoscale microscopic defects in graphene remains unexplored. Metal-organic chemical vapor deposition (MOCVD) of GaN requires high temperatures and a radical reaction environment, which can damage graphene. This study investigates the effects of chemical doping and nanoscale defects in graphene on remote epitaxy during MOCVD growth of GaN crystallites on graphene-coated Al₂O₃ for understanding the early growth stage and the resulting crystal quality. Three distinct modes are identified: remote epitaxy, anchored remote epitaxy, and epitaxial lateral overgrowth (ELOG). Pristine graphene enables pure remote epitaxy of well-aligned, strain-relaxed GaN crystallites. N-doped graphene promotes chemically anchored nucleation, causing slightly misaligned crystallites due to altered remote atomic interaction, newly termed "anchored remote epitaxy". Graphene pinholes induce direct GaN-Al₂O₃ covalent bonding for ELOG, resulting in significant compressive strain in GaN. How graphene's chemical and physical defects affect epitaxial crystallite quality (i.e., alignment, strain relaxation, density) is further explored based on bonding mechanisms, providing insights into remote epitaxy for next-generation semiconductor fabrication.