A noble method forming single crystalline AlN films has been developed as a new substrate for blue/UV light emitters. Sapphire substrates have been nitrided by appropriate CO-N-2 gas mixtures saturated with graphite based on the chemical potential diagram of the Al-N-O-C system. The nitrided surface of sapphire consists of consecutive layers of AlN and gamma-aluminum oxynitride (gamma-ALON) with low-level dislocation density, where the gamma-ALON layer spontaneously forms as an equilibrium phase and acts as a buffer. The lattice mismatch between sapphire substrate and AlN layer has been effectively reduced by using the gamma-ALON buffer, which significantly attributes to the growth of single crystalline AlN. (C) 2003 Elsevier B.V. All rights reserved.