Exciton relaxation and coupling dynamics in a GaAs/Al_xGa_(1-x)As quantum well and quantum dot ensemble

摘要

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 →QD relaxation, and weak QD→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→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 →QD relaxation rate increases with temperature, and QD → QW excitation is observed at temperatures ≥35 K.