Synchrotron x-ray topography studies of epitaxial lateral overgrowth of GaN on sapphire

Synchrotron white beam x-ray topography techniques, in section and large-area transmission modes, have been applied to the evaluation of ELOG GaN on Al2O3 Using the openings in 100 nm thick SiO2 windows, a new GaN growth took place, which resulted in typical overgrowth thicknesses of 6.8 mu m. Measurements on the recorded Laue patterns indicate that the misorientation of GaN with respect to the sapphire substrate (excluding a 30 degrees rotation between them) varies considerably along various crystalline directions, reaching a maximum of a similar to 0.66 degrees rotation of the (0001) plane about the [01.1] axis. This is similar to 3% smaller than the misorientation measured in the non-ELOG reference, which reached a maximum of 0.68 degrees. This misorientation varies measurably as the stripe or window dimensions are changed. The quality of the ELOG epilayers is improved when compared to the non-ELOG samples, though some local deviations from lattice coherence were observed. Long range and large-scale (order of 100 mu m long) strain structures were observed in all multi quantum well epilayers.