We report the epitaxial growth of a GaN epilayer on a sapphire substrate coated with platinum nanocluster (SSPN) by metalorganic chemical vapor deposition. To form the platinum nanocluster on sapphire substrate, a 5-nm-thick platinum layer was deposited by the e-beam evaporation, and then a thermal annealing process was carried out. Optical and structural properties of the GaN epilayer grown on SSPN were estimated by photoluminescence (PL), atomic force microscopy (AFM), high-resolution X-ray diffraction (HR-XRD) and transmission electron microscopy ITEM). The XRD full-width at half-maximum (FWHM) value of the (102) asymmetry plane for the GaN layer with SSPN was decreased from 390 to 320 arcsec compared to that of the GaN without SSPN, and the reduced defect-related pits on the GaN surface were observed from the AFM images. In PL, intense band-edge luminescence with narrower FWHM (38 meV) was obtained. We believe that improved quality of GaN epilayer grown on SSPN is attributed to lateral growth mode induced by thickness fluctuation of buffer zone, which is confirmed by TEM observation. (C) 2009 Elsevier B.V. All rights reserved.