All as-grown InN is n-type, with carrier concentrations typically in the range of 10(18)-10(20) cm(-3). Whether the native carrier concentration is attributable to defects, oxygen impurities, or other causes has yet to be determined. We have employed nondestructive ion beam analysis techniques to study both layer stoichiometry and oxygen content in a series of InN films grown by plasma-assisted molecular beam epitaxy on a variety of substrates. We show that not only does the InN surface readily oxidise, but a significant amount of oxygen can be drawn from the substrate as well. (c) 2006 Elsevier B.V. All rights reserved.