Structural Variants in Attempted Heteroepitaxial Growth of B₁₂As₂ on 6H–SiC (0001)

Boron sub-arsenide, B₁₂As₂, is based on twelve-atom clusters of boron atoms and two-atom As–As chains. By contrast, SiC is a tetrahedrally bonded covalent semiconductor. Despite these fundamental differences, the basal plane hexagonal lattice constant of boron sub-arsenide is twice that of SiC. This coincidence suggests the possibility of heteroepitaxial growth of boron sub-arsenide films on properly aligned SiC. However, there are a variety of incommensurate alignments by which heteroepitaxial growth of B₁₂As₂ on (0001) 6H–SiC can occur. In this study, we first used geometrical crystallographic considerations to describe the possible arrangements of B₁₂As₂ on (0001) 6H–SiC. We identified four translational and two rotational variants. We then analyzed electron backscattered diffraction and transmission electron microscopy images for evidence of distinct domains of such structural variants. Micron-scale regions with each of the two possible rotational alignments of B₁₂As₂ icosahedra with the SiC surface were seen. On a finer length scale (100–300 nm) within these regions, boron-rich boundaries were found, consistent with those between pairs of the four equivalent translational variants associated with a two-to-one lattice match. Boron-carbide reaction layers were also observed at interfaces between SiC and B₁₂As₂.