Transition from Screw-Type to Edge-Type Misfit Dislocations at InGaN/GaN Heterointerfaces

We have investigated the interface dislocations in InxGa1-xN/GaN heterostructures (0 & LE; x & LE; 0.20) using diffraction contrast analysis in a transmission electron microscope. The results indicate that the structural properties of interface dislocations depend on the indium composition. For lower indium composition (up to x = 0.09), we observed that the screw-type dislocations and dislocation half-loops occurred at the interface, even though the former do not contribute toward elastic relaxation of the misfit strain in the InGaN layer. With the increase in indium composition (0.13 & LE; x & LE; 0.17), in addition to the network of screw-type dislocations, edge-type misfit dislocations were generated, with their density gradually increasing. For higher indium composition (0.18 & LE; x & LE; 0.20), all of the interface dislocations are transformed into a network of straight misfit dislocations along the direction, leading to partial relaxation of the InGaN epilayer. The presence of dislocation half-loops may be explained by a slip on basal plane; formation of edge-type misfit dislocations are attributed to punch-out mechanism.