Exciton relaxation and coupling dynamics in a GaAs/AlxGa1−xAs quantum well and quantum dot ensemble

Abstract

Exciton inter- and intra-actions in a GaAs/AlGaAs quantum well (QW) and quantum dot (QD) ensemble are studied using optical two-dimensional Fourier transform spectroscopy. We measure population dynamics for times up to 300 ps and temperatures up to 50 K and observe biexponential decay for both QW and QD excitons, strong QW $\ensuremath{\rightarrow}$ QD relaxation, and weak QD $\ensuremath{\rightarrow}$ QW activation. The population dynamics are modeled using a system of rate equations that incorporate radiative and nonradiative decay, coupling between bright and dark exciton states, and QW $\ensuremath{\leftrightarrow}$ QD coupling. The fast decay rates are attributed to exciton-bound hole spin flips between optically active and inactive states and are similar for the QW and QDs, indicating excitons are weakly localized in the QDs. The QW $\ensuremath{\rightarrow}$ QD relaxation rate increases with temperature, and QD $\ensuremath{\rightarrow}$ QW excitation is observed at temperatures $\ensuremath{\geqslant}$35 K.