Thin films of the semiconductor scandium nitride were deposited onto sapphire substrates using reactive magnetron sputtering. Increasing concentrations of oxygen were introduced into the ScN films via increasing the residual base pressure in the deposition chamber prior to introduction of the reactive Ar/N-2 sputtering gas mixture. Films showed significant oxygen contamination even when deposited using base pressures of 10(-6) Pa. Increasing levels of contamination degrade the crystalline quality of the films. Oxygen contamination also contributes to the non-Arrhenius behaviour of film resistivity versus temperature and ultimately results in degenerate n-type conductivity in the ScN films. Oxygen incorporation in ScN increases the direct band gaps from 2.2 eV to 3.1 eV and may therefore be a contributing reason for the wide range of direct band gaps experimentally determined for this material. Comparison with TiN and ZrN films deposited under similar conditions shows that ScN displays a comparatively high oxygen affinity. The results imply that the production of ScN films possessing high crystalline quality and non-degenerate electrical properties requires the use of deposition techniques involving ultra-high vacuum conditions or other low-oxygen environments. (c) 2008 Elsevier B.V. All rights reserved.