Due to the special dislocation slip systems in hexagonal lattice, dislocation dominated deformations in hexagonal structured multilayers were significantly different from that in cubic structured systems. Here, a study was made of the strain relaxation mechanism in hexagonal-structure InGaN/AlGaN/GaN multilayers with transmission electron microscopy. Due to lattice mismatch, the strain relaxation was found to initiate with the formation of pyramidal dislocations. Such dislocations locally lay on only one preferential slip direction in the hexagonal lattice. This preferential slip caused a shear stress along the basal planes and consequently led to dissociation of pyramidal dislocations and operation of the basal plane slip system. The compressive InGaN layers and “weak” AlGaN/InGaN interfaces stimulated the dissociation of pyramidal dislocations at the interfaces. These results enhance the understanding of interactions between dislocations and layer interfaces and shed new lights on deformation mechanism in hexagonal-lattice multilayers.

Pyramidal Dislocation Induced Strain Relaxation in Hexagonal Structured InGaN/AlGaN/GaN Multilayer. P.F.Yan, K.Du, M.L.Sui: Journal of Applied Physics, 2012, 112[8], 083502