Stabilization of cubic AlN in epitaxial AlN/TiN superlattices

The high-pressure rocksalt structure of AlN was stabilized in epitaxial AlN/TiN(001) superlattices with AlN layer thickness ≤2.0 nm. The AlN layers were shown to be pure rocksalt-structure AlN, with a stress-free lattice parameter of 0.408 ± 0.002 nm, using x-ray diffraction, transmission electron microscopy, and electron energy loss spectroscopy. The stable hexagonal phase was observed for AlN layer thickness > 2 nm. The rocksalt structure formed at small layer thicknesses since it provided lower AlN/TiN interfacial energy than the hexagonal or zinc-blende structures.