Optical and structural properties of In_0.5Ga_0.5As quantum dots with different numbers of stacks grown by atomic layer molecular beam epitaxy: vertical realignment of weakly coupled quantum dots

We have investigated optical and structural properties of various In0.5Ga0.5As quantum dot (QD) structures as a function of stacking number, grown by atomic layer molecular beam epitaxy (ALE). We found that the excitation power and temperature dependence of well-separated two emissions from 10 stacked InGaAs QD samples are different from those of other QDs with the stacking numbers of 1, 3 and 5. Although the GaAs spacer thickness is ~35 nm at which the strain field penetration can be ignored for Stranski–Krastanov mode-grown InAs QDs, our ALE-grown QDs are influenced by the strain field penetration due to the larger size of ALE QDs. From transmission electron microscopic images, we observed that the ten stacked QD sample has a complex QD size distribution predominantly due to vertical size variation with stacking and that upper stacked (5–10) QD layers are vertically realigned due to the merged strain field penetration between laterally coupled QDs.