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 $\le 2.0\mathrm{nm}$. The AlN layers were shown to be pure rocksalt-structure AlN, with a stress-free lattice parameter of $0.408\pm 0.002\mathrm{nm}$, using x-ray diffraction, transmission electron microscopy, and electron energy loss spectroscopy. The stable hexagonal phase was observed for AlN layer thickness $>2\mathrm{}\mathrm{nm}$. The rocksalt structure formed at small layer thicknesses since it provided lower AlN/TiN interfacial energy than the hexagonal or zinc-blende structures.