Charging Dynamics of Single InGaAs Quantum Dots under Resonant Excitation*

Semiconductor quantum dots can act as sources of single photons, but certain experimental factors can complicate their single photon emission. Resonant excitation of either a neutral or charged quantum dot can cause a transition to the opposite charge state, which greatly diminishes the fluorescence and reduces a dot’s suitability to act as an efficient photon source. A counter to this effect is application of a low-power above-band laser that supplies the local charge environment with extra electrons and holes in the bulk material. These charge carriers can be captured by either a charged quantum dot, resulting in neutralization and allowing resonant excitation of the exciton state, or a neutral quantum dot, allowing resonant excitation of the trion state. We characterize as a function of laser power the steady-state regime and the time-dependent dynamics of a charged quantum dot by modulating the above-band laser power. The time-resolved fluorescence is recorded and phenomenological fits are used to extract the charging and discharging rates associated with the different processes that move charge carriers into and out of the quantum dot.