Atomic structure of the m-plane AlN/SiC interface

High-temperature m-plane AlN nucleation layers have been used for the growth of planar GaN films by metalorganic chemical vapor deposition on (1 0 1̄ 0) m-plane 6H-SiC substrates. Structural studies using transmission electron microscopy reveal the presence of a novel AlN intermediary layer preceding the remainder of the 2H-AlN buffer layer. High-resolution observations and image simulations indicate that this initial AlN layer has a faulted hexagonal structure with a six-layer repeating stacking sequence of ...CBCACBCBCACB... along the transverse [0 0 0 1] direction, which does not replicate the underlying 6H-SiC stacking. Based on image analysis, the space group of this novel phase is tentatively identified as P3m1, which is also hexagonal. A structural model of the m-plane AlN/SiC interface with periodic misfit defects is also proposed. Charge neutrality analysis indicates that the interface has an equal mixture of C-Al and Si-N bonds.