Ultrafast processes in quantum dot devices

The dephasing time and the population relaxation dynamics of the excitonic ground-state transitions in an electrically-pumped semiconductor optical amplifier containing InGaAs/GaAs quantum dots as active medium are measured at 10K using a highly sensitive heterodyne technique. Electrical injection into the barrier region results in a pure dephasing of the excitonic transitions. Once the injected carriers have filled the electronic ground state, additional filling of the excited states creates multiexcitons that show a fast dephasing due to population relaxation.