Ultralow-temperature ultrafast formation of single-crystalline graphene via metal-assisted graphitization of silicon-carbide

Non-conventional epitaxial techniques, such as van der Waals epitaxy (vdWE) and remote epitaxy, have attracted substantial attention in the semiconductor research community for their exceptional capability to continuously produce high-quality free-standing films on a single mother wafer without needing surface refurbishment. The successful implementation of these emerging epitaxial techniques crucially hinges on creating a robust uniform two-dimensional (2D) material surface at the wafer-scale and with atomically precise uniformity. The conventional method for fabricating graphene on a silicon carbide (SiC) wafer is through high-temperature graphitization, which produces epitaxial graphene on the surface of the SiC wafer. However, the extremely high temperature needed for silicon sublimation (typically above 1500°C) causes step-bunching of the SiC surface in addition to the growth of uneven graphene at the edges of the step, leading to multilayer graphene stripes and unfavorable surface morphology for epitaxial growth. Here, we fully develop a graphitization technique that allows fast synthesis of single-crystalline graphene at ultra-low temperatures (growth time of less than 1 minute and growth temperature of less than 500°C) at wafer-scale by metal-assisted graphitization (MAG). We found annealing conditions that enable SiC dissociation while avoiding silicide formation, which produces single-crystalline graphene while maintaining atomically smooth surface morphology. The thickness of the graphene layer can be precisely controlled by varying the metal thickness or annealing temperature, allowing the substrate to be utilized for either a remote epitaxial growth substrate or a vdWE growth substrate, depending on the thickness of the graphene. We successfully produce freestanding single-crystalline ultra-wide bandgap (AlN, GaN) films on graphene/SiC via the 2D material-based layer transfer (2DLT) technique. The exfoliated films exhibit high crystallinity and low defect densities. Our results show that low-temperature graphene synthesis via MAG represents a promising route for the commercialization of the 2D-based epitaxy technique, enabling the production of large-scale ultra-wide bandgap free-standing crystalline membranes.