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

The growth and defect structures in free-standing self-assembled In0.6Ga0.4 As quantum dots (QDs) grown on (001) GaAs by solid source molecular beam ep itaxy has been investigated. The QDs are elongated along [(1) over bar 1 0] , At a nominal thickness of eight monolayers defect complexes, associated w ith intrinsic stacking faults, have been generally observed on both sides o f a QD in ((1) over bar 1 0) cross-section. The total defect vector of such defect complexes is a/3 [111]. Local strain components on {111} slip plane s in the QDs without defects have been measured directly from digitized hig h-resolution electron microscopy images. The distortion on the two sets of {111} planes of a ((1) over bar 1 0) cross-section is different owing to el astic relaxation, The results of strain measurements suggest that a 60 degr ees dislocation nucleates first on the set of {111} planes of higher contra ctive shear strain, i.e. (111) planes on the right side of the QDs, and ((1 ) over bar (1) over bar 1) planes on the left side, A 30 degrees partial di slocation forms subsequently on the other set of {111} planes, i.e. ((1) ov er bar (1) over bar 1) planes on the right side of the QDs and (111) planes on the left side, when the 60 degrees dislocation glides down towards the In0.6Ga0.4As/GaAs interface, as a result of the additional strain field of the 60 degrees dislocation, The efficiency of the defect complexes in strai n relaxation of the QDs has been shown by strain measurements in QDs with t he presence of defects.