Effect of anneal duration on GaN nuclei and subsequent epilayers

The effect of nucleation morphology on GaN epilayer structural characteristics has been investigated, as these are revealed by both symmetric and asymmetric x-ray diffraction rocking curve scans. To this end, epilayers deposited by metalorganic vapour phase epitaxy under identical conditions on a series of nucleation layers that were subjected to anneal for varying lengths of time, have been used. It is shown that nucleation layers subjected to extended anneal have narrower nuclei diameter distributions and yield epilayers with higher values of twist (and thus edge dislocation density), but with lower values of tilt, and, consequently, narrower peak widths for symmetric or low inclination lattice plane X-ray reflections. It is thus indicated that for optimization experiments of this kind, the widths of rocking curves obtained from symmetric or low inclination angle reflections are misleading as a guide to the structural quality of the deposited epilayers.