Coulomb and carrier-activation dynamics of resonantly excited InAs/GaAs quantum dots in two-color pump-probe experiments

We study Coulomb and carrier dynamics in self-assembled InAs/GaAs quantum dots at room temperature by two-color tunable differential transmission experiments, with resonant excitation in the ground state. Coulomb renormalization of the first excited state in the presence of one electron-hole pair in the ground state manifests as a 6-meV redshift. Several time scales for carrier activation to the first excited state are distinguished, corresponding to activation processes occurring in singly and doubly occupied dots, including carrier thermalization. Electron thermal activation occurs on a 250 ps time scale, confirming the absence of a phonon bottleneck at room temperature.