Heteroepitaxial growth of indium. nitride (InN) film crystal on ZnO single crystals was examined. InN films were grown on c(+)- and c(-)-ZnO single crystal substrates by molecular beam epitaxy using an RF plasma cell as a nitrogen source. InN films on c(+)-ZnO had a columnar structure with low crystallinity, while those on c(-)-ZnO were single crystalline films in which the full-width-at-half-maxima of their 0002 rocking curves were about 150 arcsec. The polarity dependence of the film crystallinity is discussed in terms of the reactivity at the InN/ZnO interface. (c) 2006 Elsevier B.V. All rights reserved.