InN films were grown by N-2 plasma-assisted molecular beam epitaxy on Al2O3 substrates with GaN buffer layers at different substrate temperatures from 200 to 500 degrees C. It was found that the crystal quality of InN films was improved with growth temperature. The optical absorption edge of InN films decreased from 1.8 to 1.1 eV with increasing substrate temperature from 200 to 500 degrees C. Photoluminescence measurement on InN films grown at 500 degrees C exhibited the band-edge emission at around 1.0-1.1 eV. (c) 2006 Elsevier B.V. All rights reserved.