Investigation of the dimensionality using temperature-dependent decay times in InGaAs-coupled quantum well-quantum dots structures

The radiative temperature-dependent decay times were exploited to understand the confinement size analyzing the relaxation from thermally-excited states in InGaAs coupled quantum well (QW)–quantum dots (QDs) structures. We investigated the confinement size from coupled QW-QDs structures by measuring the decay time of radiative process from exciton states when the temperature is gradually increased. The photoluminescence (PL) decay time from the exciton states is amended with the PL intensity at low temperature (~5 K) to distinguish the radiative decay time. The zero-dimensional and the two-dimensional confinement size are obtained from the isolated QDs and QW. However, this assumption is no longer correct for optical coupling because of the direct tunneling when the distance between the QW and the QDs becomes less than 10 nm in the coupled QW-QDs structures. Below 6 nm between the QW and the QDs in the coupled QW-QDs structures, the power factor from the temperature variations increases from 0 to 0.3 (for QDs) and from 1 to 1.37 (for QW), which accords with a quasi-zero-dimensional density of states (~T^α=0.3) and a quasi-two-dimensional density of states (~T^α=1.37), respectively, because of the extended wave functions in the optical couplings and the existence of dark states in the coupled QW-QDs structures.