Cross-sectional transmission electron microscopic observation was performed in detail to analyze the morphology of threading dislocations in GaN thin layers with various thicknesses. The GaN layers were overgrown on an Al0.28Ga0.72N layer by the metal-organic vapour-phase epitaxy method. In a GaN layer about 50nm in thickness, threading dislocations running up in the AlGaN layer pass into the GaN layer and most of them reach the top surface without bending. In thicker GaN layers, on the other hand, many of threading dislocations form a hairpin-configuration on or above the interface of GaN and AlGaN to be annihilated. This difference in morphology of threading dislocations indicated that the threading dislocations had moved down inside the GaN layer. Since the formation of hairpins was attributed to a stress-relief, there should be an extra half-plane between the paired threading dislocations. Therefore, the movement of threading dislocations should be of “climb motion”. Another example of possible threading dislocation movement inside a GaN layer was also described. It was emphasized that the possibility of threading dislocation movements inside the thin film crystal during the growth should be taken into account in analysis of thin-layer growth through the behavior of threading dislocations.

Evidence for Moving of Threading Dislocations during the VPE Growth in GaN Thin Layers. N.Kuwano, H.Miyake, K.Hiramatsu, H.Amano, I.Akasaki: Physica Status Solidi C, 2011, 8[5], 1487–90