A gallium nitride (GaN) epitaxial layer was grown by metal-organic chemical vapor deposition (MOCVD) on Si (111) substrates with aluminum nitride (AIN) buffer layers at various thicknesses. The AIN buffer layers were deposited by two methods: radio frequency (RF) magnetron sputtering and MOCVD. The effect of the AIN deposition method and layer thickness on the morphological, structural and optical properties of the GaN layers was investigated. Field emission scanning electron microscopy showed that GaN did not coalesce on the sputtered AIN buffer layer. On the other hand, it coalesced with a single domain on the MOCVD-grown AIN buffer layer. Structural and optical analyses indicated that GaN on the MOCVD-grown AIN buffer layer had fewer defects and a better aligned lattice to the a- and c-axes than GaN on the sputtered AIN buffer layer. (c) 2009 Elsevier B.V. All rights reserved.