We present an extensive study on the structural, electrical and optical properties of InN thin films grown on c-Al 2O 3, GaN(130 nm)/Al 2O 3, GaN(200 nm)/Al 2O 3 and GaN(4 μm)/Al 2O 3 by using plasma-assisted molecular beam epitaxy. The high resolution X-ray diffraction study reveals better crystalline quality for the film grown on GaN(4 μm)/Al 2O 3 as compared to others. The electronic and optical properties seem to be greatly influenced by the structural quality of the films, as can be evidenced from Hall measurement and optical absorption spectroscopy. Kane's k.p model was used to describe the dependence of optical absorption edge of InN films on carrier concentration by considering the non-parabolic dispersion relation for carrier in the conduction band. Room temperature Raman spectra for the InN films grown on GaN show the signature of residual tensile stress in contrast to the compressive stress observed for the films grown directly on c-Al 2O 3. © 2012 Elsevier B.V.