Surface and interface control in the epitaxial growth of boride thin films

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A unique ultrahigh vacuum chemical vapor epitaxy system, which prevents oxygen incorporation into boride films and also has capability of in-situ growth monitoring, was successfully built. The epitaxial growth of zirconium diboride thin films was carried out on silicon, sapphire, and gallium nitride. Surface segregating elements originating from the substrates, which were observed as different surface reconstructions during the growth, were found to be responsible for the reaction at the surface. Single-crystallinity was confirmed for the films grown on sapphire substrates under optimized conditions, driven by a stable interface structure, while the films grown on silicon contained some misoriented crystallites due to competing interfaces.