Transmission electron microscopy was used to study the relaxation of misfit strains in GaN/Al0.28Ga0.72N layers grown on (00•1) sapphire. It was observed that threading edge-type dislocations migrate laterally in the top GaN layer to form misfit dislocations. This led to reactions with other threading dislocations, to generate either closed loops or more complex nodes, which reduced the total threading dislocation density. The proportion of edge-type dislocations compared to screw-type and mixed dislocations was reduced with increasing GaN thickness. It was proposed that the lateral migration of the dislocations was predominantly by a climb rather than a glide mechanism.

Migration of Dislocations in Strained GaN Heteroepitaxial Layers. S.L.Sahonta, M.Q.Baines, D.Cherns, H.Amano, F.A.Ponce: Physica Status Solidi B, 2002, 234[3], 952-5

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