A correlation between the structural and optical properties of GaN thin films grown in the [11 2- 0] direction has been established using transmission electron microscopy and cathodoluminescence spectroscopy. The GaN films were grown on an r -plane sapphire substrate, and epitaxial lateral overgrowth was achieved using Si O2 masks. A comparison between the properties of GaN directly grown on sapphire and GaN laterally grown over the Si O2 mask is presented. The densities and dimensions of the stacking faults vary significantly with a high density of short faults in the window region and a much lower density of longer faults in the wing region. The low-temperature luminescence spectra consist of peaks at 3.465 and 3.41 eV, corresponding to emission from donor-bound excitons and basal-plane stacking faults, respectively. A correlation between the structural defects and the light emission characteristics is presented. © 2008 American Institute of Physics.