Thin films of GaAsxN1-x alloys were deposited by reactive rf magnetron sputtering of GaAs target with a mixture of argon and nitrogen as the sputtering gas. Growth rate was found to decrease from similar to 7 mu m/h to similar to 2 mu m/h as the nitrogen content increased from 0% to 40%. XRD and TEM studies of the films reveal the presence of hexagonal GaN with a significant increase of the lattice parameters in a narrow range of composition of the sputtering gas (5-10% nitrogen), which is attributed to the incorporation of arsenic. The limited availability of nitrogen in the sputtering atmosphere is found to encourage the incorporation of arsenic in the alloy films. Optical absorption coefficient spectra of the films were obtained from reflection and transmission data. The effect of arsenic incorporation is seen in the optical absorption spectra of the films, which show a continuous shift of the absorption edge to lower energies with respect to that of gallium nitride. (c) 2006 Elsevier B.V. All rights reserved.