Extended dimensionality of the density of states in InGaAs coupled quantum dot-ring structures as evidenced by radiative decay times

We observed radiative decay times as a function of temperature by analyzing the thermal relaxation from the excited exciton states in InGaAs coupled quantum dot (QD)–quantum ring (QR) structures. To investigate the confinement of electron-hole pair wavefunctions in the coupled QD-QR structures, we measured radiative decay times with temperature, where the photoluminescence decay time of electron-hole pairs was corrected based on the relative photoluminescence intensity at 4 K to discriminate the radiative processes. For decoupled QRs and QDs, quasi-one dimensional (for QRs) and zero-dimensional (for QDs) densities of states have been reported. However, dimensional densities of states from decoupled QRs and QDs do not apply when the distance between QRs and QDs is sufficiently close in the coupled QD-QR structure owing to coupling interactions (both short- and long-range). In the present coupled structure, QD and QR is connected at the bottom, and the top side peak-to-peak distance is approximately 24 nm. Based on our observations, the power order of temperature dependence increased from 0 to 0.33 (for QDs) and from 0.7 to 1.32 (for QRs), corresponding to the quasi-zero-dimensional (∼T^α=0.33) and quasi-two-dimensional (∼T^α=1.32) confinement state, respectively, owing to amended wavefunctions of electron-hole pairs and dark states effect.