Misfit dislocation generation in InGaN epilayers on free-standing GaN

We have found that, in the absence of threading dislocations in InxGa1-xN/GaN heterostructures, coherent generation of misfit dislocations occurs for x > 0.11 in similar to 100-nm-thick epilayers. We focus this report on In0.17Ga0.83N grown on a low-defect-density GaN free-standing substrate (with 1.9% lattice mismatch). A diffraction contrast analysis carried out in the transmission electron microscope showed straight line defects with Burgers vectors 2/3 (11(2)over bar0) (i.e., 2a, where a is the hexagonal plane lattice parameter), which extended many micrometers approximately along (1(1)over bar00) directions and with an average lateral spacing of 90 nm. Although these defects were complex and mostly sessile, evidence was found that they can dissociate into glissile misfit dislocations with Burgers vectors of 1/3 (11(2)over bar0). It is proposed that the defects are generated by a punch-out mechanism involving slip on inclined prismatic planes. The properties of these defects and their role in relieving misfit strains are discussed.