Spin-preserving ultrafast carrier capture and relaxation in InGaAs quantum dots

Carrier capture into self-organized $InGaAs∕GaAs$ quantum dots with an electronic level spacing close to optical phonon energies is studied in a two-color femtosecond transmission experiment. After resonant generation of carriers in the wetting layer, we analyze the population of both the band edge of the wetting layer and the excited states of the quantum dots. Most strikingly, the carrier capture time of 3 ps is found to be independent of the carrier density, providing that it remains small compared to the number of available electronic states in the quantum dots. Moreover, we find that the capture process is predominantly spin preserving in nature. These results suggest that phonon-mediated scattering governs the quantum dot filling.