Carrier capture and relaxation through a continuum background in InAs quantum dots

Carrier capture and relaxation in self-assembled InAs/GaAs quantum dots (QDs) have been studied, using bleaching rise time measurements for both the ground state (GS) and the first excited state (ES) transition, as a function of temperature (5, 77 and 293 K) and excitation density. We surprisingly observe that the bleaching rise time is longer for the ES than for the GS, indicating that the ES does not act as an intermediate state. At intermediate excitation density where the carrier relaxation is usually explained by Auger scattering, we still observe a temperature dependence pointing towards a single phonon emission process. 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 towards a relaxation through the continuum background, followed by a single LO-phonon emission towards the QD GS.