Indium nitride (InN) films were prepared by a radio frequency magnetron sputtering in N-2/Ar mixed gases. The results on X-ray diffraction measurements indicated that all of the InN films deposited were hexagonal crystalline InN. The c-axis lattice constant of the InN film deposited at room temperature was decreased with the increase of Ar composition ratio in N-2/Ar mixed gas. For the InN film deposited in pure N-2 gas it was also decreased with the increase of substrate temperature, which was related to the relative nitrogen concentration in the InN film. The results on X-ray diffraction and Raman spectroscopy measurements indicated that the InN films with large c-axis lattice constant were disordered crystalline film and had nitrogen-rich stoichiometry. The optical band-gap energies of the disordered InN films were always large values of 1.42-1.85 ev, whereas that of high quality InN film deposited on GaN/Al2O3 substrate at 450 degrees C in pure N-2 gas, was 0.84 eV (c) 2005 Elsevier B.V. All rights reserved.