Time-resolved emission from self-assembled single quantum dots using scanning near-field optical microscope

We study time-resolved emission from self-assembled single InGaAs/GaAs quantum dots by the time-correlated single photon counting method using near-field optical microscopy. The decay time of the emission from discrete levels of a single quantum dot increases with the decrease in the emission energy and with the increase in the excitation intensity. We develop a rate equation model which accounts for the initial filling of the states, cascade relaxation, state filling and carrier feeding from a wetting layer. High collection efficiency of a double-tapered-type fiber probe enables us to study the emission even at very weak excitation intensities. The direct excitation into a single dot is dominant at this excitation level. State filling, cascade relaxation and extra carrier feeding from the wetting layer become pronounced when the excitation intensity increases.