Epitaxial lateral overgrowth of GaN on Al2O3 Using a SiO2 mask with different fill factors (ratio of stripe opening width to stripe period) is examined with synchrotron X-ray topography (SXRT) and X-ray diffraction (XRD) techniques. The crystal misorientation in the lateral overgrown region (wing) and the normal region (window region and beneath the seed layer) is determined with SXRT. The wings tilt asymmetrically around the window and the tilts increase as the fill factor increases. XRD measurements confirm the same wing tilt tendency as the fill factor changes. The average wing tilt reaches approximately 1600 arcsec measured using the X-ray rocking curve method at a fill factor of 0.625, but the maximum wing tilts can reach values as large as 2400 arcsec: measured by SXRT when the fill factor is only 0.571. The significance of this is explained. The crystal misorientation in the normal region is approximately an order of magnitude less than the wing tilt. (C) 2002 Elsevier Science B.V. All rights reserved.