A transmission electron microscopy study of defects formed through the capping layer of self-assembled InAs/GaAs quantum dot samples

Plan-view and cross-sectional transmission electron microscopy have been used for a detailed study of the defects formed in capped InAsGaAs quantum dot (QD) samples. Three main types of defects, V-shaped defects, single stacking faults, and stacking fault pyramids, were found to form under growth conditions that led to either very large, indium enriched, or coalesced islands. All three types of defects originate at the buried quantum dot layer and then travel through the GaAs cap to the surface on the {111} planes. The V-shaped defects were the most common and typically consisted of two pairs of closely spaced 60° Shockley partials with a 〈211〉 line direction. The two pairs originate together at the buried QD layer and then travel in "opposite" directions on different {111} planes. The second type of defect is the single stacking fault which consists of a single pair of partial dislocations separated by an ≈50 nm wide stacking fault. Finally, both complete and incomplete stacking fault pyramids were observed. In the case of the complete stacking fault pyramid the bounding dislocations along the [110], [1 1- 0], [10 1-], and [101] directions were identified as stair rods. A possible mechanism for the stacking fault pyramid formation, which can also account for the creation of incomplete stacking fault pyramids, is presented.