The GaN layer grown by epitaxial lateral overgrowth on sapphire (0001) has been investigated by synchrotron X-ray diffraction. The results show that ELO GaN stripes bend towards the SiN x mask in directions perpendicular to the stripe direction. This lead to the GaN (0001) crystal planes in the ’ wings’ (overgrown GaN) exhibit crystallographic tilts away from those in the ’ window’ (seed) regions. The GaN (0002) diffraction was used to determine the grain sizes in the wing region and window region

respectively. It is found that the grain size in the wing region increases about three times comparing to those in window region.