The electron cyclotron resonance plasma-enhanced metalorganic chemical vapor deposition technology (ECR-MOPECVD) is adopted to grow GaN films on (0 0 0 1) alpha-Al2O3 substrate. The gas sources are pure N-2 and trimethylgallium (TMG). Optical emission spectroscopy (OES) and thermodynamic analysis of GaN growth are applied to understand the GaN growth process. The OES of ECR plasma shows that TMG is significantly dissociated in ECR plasma. Reactants N and Ga in the plasma, obtained easily under the self-heating condition, are essential for the GaN growth. They contribute to the realization of GaN film growth at a relatively low temperature. The thermodynamic study shows that the driving force for the GaN growth is high when N-2:TMG > 1. Furthermore, higher N2:TMG flow ratio makes the GaN growth easier. Finally, X-ray diffraction, photoluminescence, and atomic force microscope are applied to investigate crystal quality, morphology, and roughness of the GaN films. The results demonstrate that the ECR-MOPECVD technology is favorable for depositing GaN films at low temperatures. (C) 2009 Elsevier B.V. All rights reserved.