The generation of misfit dislocations in facet-controlled growth of AlGaN/GaN films

The relaxation of tensile stresses in AlGaN layers grown on GaN/(0001)sapphire by facet-controlled epitaxial lateral overgrowth is reported. It is shown that a-type misfit dislocations are introduced at inclined {11 (2) over bar2} AlGaN/GaN interfaces, with strong evidence for a half-loop nucleation and glide mechanism driven by shear stresses present on the (0001) slip plane. In addition to relieving misfit stresses, these dislocations introduce grain rotations of up to 10(-2) rad across the AlGaN/GaN boundaries, leading to tilt boundaries at the meeting front between laterally growing wings and between regions growing in the lateral and [0001] directions. The effects of these processes on the defect density in subsequent layers are examined.