GaN films were grown on sapphire substrates by laser-induced reactive epitaxy. The domains in the films were determined to be the Ga-polarity by the convergent beam electron diffraction (CBED) technique, while the adjacent matrices had the N-polarity. The domain boundaries were characterized as inversion domain boundaries (IDBs). An atomic structure of the IDB is proposed based on high-resolution transmission electron microscopy (HRTEM) investigations. Control of the polarity of GaN/ sapphire films was achieved by suppressing the formation of IDBs with an interlayer of A1GaN and a low-temperature GaN buffer layer. (c) 2005 Elsevier B.V. All rights reserved.