Boron-Assisted Epitaxial Growth of Buffer-Layer-Free Graphene on the Si-Face of SiC without 30° Rotation

Graphene grown by thermal decomposition of SiC has attracted significant attention due to its scalability and direct synthesis on the wide-bandgap semiconductor substrate. Conventional epitaxial growth on the Si-face of 4H-SiC typically results in 30°-rotated (R30) graphene that is strongly coupled to the substrate via a buffer layer that is a deformed honeycomb lattice of carbon exhibiting a (6√3 × 6√3)R30° periodicity. Here, we report an epitaxial growth mode enabled by boron, resulting in graphene without 30°-rotation (R0) and without the formation of the buffer layer between graphene and SiC. This growth occurs at relatively low temperatures (∼1450 °C) despite the use of an Ar atmosphere. The number of layers of R0-aligned graphene varies depending on the growth temperature, but all layers exhibit no detectable rotational misalignment, as confirmed by reflection high-energy electron diffraction (RHEED) and transmission electron microscopy (TEM). TEM also reveals an enlarged interlayer spacing around 3.5 Å and non-Bernal, translationally random stacking indicative of weakened interlayer coupling. Electron energy loss spectroscopy (EELS) shows a high concentration of boron confined to the graphene/SiC interface and a smaller amount within the graphene layers. Raman spectroscopy confirms the absence of the buffer layer and indicates that substitutional boron, if present, accounts for only a small fraction of the total boron. These results demonstrate that boron-assisted growth fundamentally alters the interfacial chemistry and stacking sequence of epitaxial graphene on SiC, enabling R0-aligned, buffer-layer-free multilayer graphene.