Carrier transfer and redistribution dynamics in vertically aligned stacked In0.5Ga0.5As quantum dots with different GaAs spacer thicknesses

Abstract

We have investigated optical and structural properties of three-stacked InGaAs quantum dot (QD) structure with GaAs spacer thicknesses of 22, 35, and 88 nm (denoted by QD22, QD35, and QD88, respectively) grown by migration-enhanced molecular beam epitaxy. From temperature-dependent photoluminescence (PL) analysis, it is found that thermal carrier redistribution between vertically adjacent QD layers plays an important role as the thickness of GaAs spacer is reduced from 88 to 22 nm. Although the QD sizes of upper layers are quite similar to those of the first bottom layer, the QDs of the upper layers appear to emit at higher energies probably due to different alloy compositions caused by the strain-induced intermixing effect between InGaAs QDs and GaAs barriers with stacking. Especially for QD22 sample, we observed thermally assisted carriers transfer among vertically adjacent QD layers with increasing temperature by using time-resolved PL measurements, which is in good agreement with the temperature dependence of integrated PL intensity and peak energy position.