Radiative and non-radiative relaxation of excitons in strain-compensated quantum dots

We have investigated the population dynamics of excitons in strain-compensated InAs quantum dots (QDs) using a pump–probe technique under resonant excitation. Precise control of polarization directions of incident pulses enabled us to selectively estimate population lifetimes for two orthogonally polarized exciton ground states according to polarization selection rules. Measured decay times of the probe transmissions were highly dependent on the polarization directions of the exciton states. We found that the ratio of the decay times for the orthogonally polarized states is in quantitative agreement with the ratio of square of the transition dipole moments. This indicates that radiative recombination processes have a dominant effect on the population dynamics and that non-radiative and spin relaxations are negligible in our QDs. As a result, we can estimate the radiative lifetimes to be 1.0±0.1 and 1.7±0.2 ns for orthogonally polarized exciton ground states.