GaN thin films have been grown on Si(111) substrates using an atomic layer deposition (ALD)-grown Al2O3 interlayer. This thin Al2O3 layer reduces strain in the subsequent GaN layer, leading to lower defect densities and improved material quality compared to GaN thin films grown by the same process on bare Si. XRD omega-scans showed a full width at half maximum (FWHM) of 549 arcsec for GaN grown on bare Si and a FWHM as low as 378 arcsec for CaN grown on Si using the ALD-grown Al2O3 interlayer. Raman spectroscopy was used to study the strain in these films in more detail, with the shift of the E-2(high) mode showing a clear dependence of strain on Al2O3 interlayer thickness. This dependence of strain on Al2O3 thickness was also observed via the redshift of the near bandedge emission in room temperature photoluminescence (RT-PL) spectroscopy. The reduction in strain results in a significant reduction in both crack density and screw dislocation density compared to similar films grown on bare Si. Screw dislocation density of the films grown on Al2O3/Si substrates approaches that of typical GaN layers on sapphire. This work shows great promise for the use of oxide interlayers for growth of GaN-based LEDs on Si. (C) 2009 Elsevier B.V. All rights reserved.