Optical and structural properties ofIn0.5Ga0.5As quantum dots with different numbers of stacks grown by atomic layer molecular beamepitaxy: vertical realignment of weakly coupled quantum dots

Abstract

We have investigated optical and structural properties of variousIn0.5Ga0.5As quantum dot (QD) structures as a function of stacking number, grown by atomic layer molecularbeam epitaxy (ALE). We found that the excitation power and temperature dependence ofwell-separated two emissions from 10 stacked InGaAs QD samples are different from those ofother 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–Krastanovmode-grown InAs QDs, our ALE-grown QDs are influenced by the strain field penetrationdue to the larger size of ALE QDs. From transmission electron microscopic images, weobserved that the ten stacked QD sample has a complex QD size distributionpredominantly 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 betweenlaterally coupled QDs.