Excitonic lifetimes in single GaAs quantum dots fabricated by local droplet etching

The time-dependent optical emission of GaAs quantum dots (QDs) is studied using single-dot photoluminescence (PL) spectroscopy with quasi-resonant excitation into the QD d-shell. The QDs are fabricated with a very recently developed method, i.e. by local droplet etching of self-assembled nanoholes in an epitaxial AlAs/AlGaAs heterostructure surface and subsequent filling with GaAs. The PL data are interpreted in terms of a three-level rate model, which yields lifetimes of 390 and 426 ps for the excitons and biexcitons, respectively. The strong dependences of both the PL peak intensities and decay times on the excitation power are quantitatively reproduced by the model. The comparison with various other types of self-assembled QDs shows the trend of a decreasing exciton lifetime with increasing emission energy. This behavior and the short lifetime of the GaAs QDs are discussed on the basis of common models of the exciton radiative lifetime.