GaN/InN alloy system has attracted an intense interest in high-temperature and high-frequency optoelectronic applications. InGaN can provide a spectral coverage from the near UV to the near IR. Due to the large lattice mismatch between InGaN and sapphire substrates, InGaN is usually deposited on the thick GaN film previously grown on GaN buffer layer on sapphire. The growth of GaN and InGaN films was studied systematically. Crystal quality, optical and electrical properties will be reported using several post-growth analysis techniques, including Rutherford back scattering (RBS), Photoluminescence (PL), absorption spectroscopy and X-ray diffraction (XRD). The effect of temperature and buffer layer annealing time on the film properties were determined. This understanding will lead to better quality control of the optoelectronice devices. (C) 2004 Elsevier B.V. All rights reserved.