Effect of Ni-Cu substrates on phase selection of hexagonal and cubic boron nitride thin films

In this study, the dependence of the phase selection of BN on the lattice parameter and the crystal structure of the substrate was clarified. BN thin film was prepared by reaction RF sputtering method on polycrystalline Ni-Cu complete solid solution alloy. Using empirical potentials, the polytypes of BN thin films were systematically investigated by considering lattice constraint due to various interface atomic arrangements and orientations such as c-BN or h-BN on cubic (0 0 1) or (1 1 1) substrates. From IR spectrum, merely c-BN phase was observed from the specimen on Cu and Ni0.8-Cu0.2 alloy. Moreover, the empirical potential calculations reveal that c-BN thin films on (0 0 1) substrates can be stabilized in the substrate lattice parameter of 3.2 < a <4.4 Å including Cu and Ni at both thin film and interface regions. From these experimental and calculated results, the strain energy at the semiconductor-metal interface proved to be dominant factor for the phase selection of BN thin films.