Role of the continuum background for carrier relaxation in InAs quantum dots

We study the carrier capture and relaxation in self-assembled InAs/GaAs quantum dots (QDs) using bleaching rise time measurements as a function of the excitation density, at 5, 77, and 293 K . We observe that the bleaching rise time and the carrier lifetime of the first excited state are longer than the bleaching rise time of the QD ground state, indicating that the excited state does not act as an intermediate state. For high excitation density, we observe a temperature-dependent plateau in the initial bleaching rise time, contradicting an Auger-scattering-based relaxation model. Both these experimental results point toward a relaxation through the continuum background, followed by a single LO-phonon emission toward the QD ground state. The relaxation through the continuum background is governed by Coulomb or acoustic phonon coupling between the continuum and the discrete QD energy levels