Defect formation in self-assembling quantum dots of InGaAs on GaAs: a case study of direct measurements of local strain from HREM

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SummaryThe growth and defect structures in free-standing self-assembled In0.6Ga0.4As quantum dots (QDs) grown on (001) GaAs by solid source molecular beam epitaxy has been investigated. The QDs are elongated along [10]. At a nominal thickness of eight monolayers defect complexes, associated with intrinsic stacking faults, have been generally observed on both sides of a QD in (10) cross-section. The total defect vector of such defect complexes is a/3 〈111〉. Local strain components on {111} slip planes in the QDs without defects have been measured directly from digitized high-resolution electron microscopy images. The distortion on the two sets of {111} planes of a (10) cross-section is different owing to elastic relaxation. The results of strain measurements suggest that a 60° dislocation nucleates first on the set of {111} planes of higher contractive shear strain, i.e. (111) planes on the right side of the QDs, and (1) planes on the left side. A 30° partial dislocation forms subsequently on the other set of {111} planes, i.e. (1) planes on the right side of the QDs and (111) planes on the left side, when the 60° dislocation glides down towards the In0.6Ga0.4As/GaAs interface, as a result of the additional strain field of the 60° dislocation. The efficiency of the defect complexes in strain relaxation of the QDs has been shown by strain measurements in QDs with the presence of defects.

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