Heteroepitaxy of Diamond on Cubic Boron Nitride

The epitaxial growth process of diamond from the gas phase on a cubic boron nitride (c-BN) {111} surface has been investigated. At the initial growth stage, carbon adsorption progressed on a boron-terminated surface of c-BN ({111}_B). The coordination of the carbon atoms was found to be the same as that observed in diamond, as confirmed by electron energy loss spectroscopy (EELS). The epitaxial growth of diamond particles has been observed after formation of the carbon layer. On the other hand, on the nitrogen-terminated surface ({111}_N), neither stable adsorption of carbon nor nucleation of diamond has been observed. The stability of adsorbed carbon atoms in the chemical vapor deposition (CVD) ambient, in which large amounts of atomic hydrogen are supplied to the substrate heated at high temperature, is quite important for the nucleation of diamond. Using cross-sectional transmission electron microscopy (TEM), numerous crystal defects were observed, both in c-BN and diamond. Formation of the epitaxial diamond particles has been observed especially at defect sites on c-BN. The misfit dislocation has been observed near the interface with the diamond particle. Even though there exist misfit dislocations that relieve the stress caused by the lattice mismatch between diamond and c-BN, the epitaxial film involved retains a tensile strain of about 0.29% for a film thickness of about 200 nm.