GaN films were deposited by hydride vapor phase epitaxy with and without adopting growth interruption modulation (GM. The surface morphologies of these samples were observed by atomic force microscopy. After chemical etching, the surface morphology of GaN film grown directly on sapphire changed greatly and turned out to be N-polarity, which could be changed into Ga-polarity when growing via interruption modulation. Photoluminescence spectra showed that optical property of Ga-polar film was better than that of N-polar film. High resolution X-ray diffraction revealed the high crystalline quality GaN film grown by using the GIM method. The polarity conversion was the result of surface reconstruction when adopting GIM method. (c) 2007 Elsevier B.V. All rights reserved.