The growth of the high-quality GaN grain on a r-plane sapphire substrate was effected by using a self-organized SiN interlayer as a selective growth mask. Transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy were used to reveal the effect of SiN on the overgrown a-plane GaN growth. The SiN layer effectively terminated the propagation of the threading dislocation and basal plane stacking faults during a-plane GaN re-growth through the interlayer, resulting in the window region shrinking from a rectangle to a "black hole". Furthermore, strong yellow luminescence in the non-polar plane and very weak yellow luminescence in the semi polar plane on the GaN grain was revealed by cathodoluminescence, suggesting that C-involved defects were responsible for the yellow luminescence.

Luminescence of a GaN Grain with a Nonpolar and Semipolar Plane in Relation to Microstructural Characterization. X.W.Zhou, S.R.Xu, J.C.Zhang, J.Y.Dang, L.Ling, H.Yue, L.X.Guo: Chinese Physics B, 2012, 21[6], 067803