Photon echo study of excitons and excitonic complexes in self-assembled quantum dots

The authors have studied the excitons and excitonic complexes in two kinds of self-assembled quantum dots (QDs) using photon echo measurements. In GaAs strain-induced quantum dots (SIQDs), a pronounced biexcitonic beat with a period of 1 ps is observed. The biexciton binding energy in SIQDs is obtained from the beat period, and its magnetic field dependence is investigated. It is found that the biexciton binding energy is remarkably increased by the lateral confinement and they are almost independent of the applied magnetic field up to 8 T. A theoretical calculation of the biexciton binding energy in SIQDs is presented to explain the observed magnetic field dependence. In charge-tunable InP QDs, the photon echo signal shows dramatic changes depending on the electric bias. The decay profile of the echo intensity is not a single exponential but Gaussian-like function, which indicates non-Markovian nature of the dephasing process in this system. Theoretical calculation is done assuming tunneling induced dephasing mechanism, and it reproduces the experimental results quite well.