Formation and evolution of misoriented grains in a-plane oriented gallium nitride layers

Annealed low-temperature GaN layers grown on r-plane sapphire substrates were examined by X-ray diffraction pole figure measurements. The GaN layers were mainly a-plane oriented, in which misoriented grains with four different orientations were detected. The c-axes of the misoriented grains are tilted from the surface normal by about 35°, which are along the bonds not parallel to the c-axis of the a-plane oriented layers. There was a difference among the peak intensities corresponding to the c-planes of the misoriented grains with the four different orientations. Considering the difference, the relative amount of misoriented grains with each orientation can be predicted. The evolution of the misoriented grains is expected to be controlled by the major polarity.