Dynamic saturation of an intersublevel transition in self-organized InAs/In_xAl_1−xAs quantum dots

We have observed a dynamic saturation of an intersublevel transition in InAs/In_xAl_1−xAs quantum dots related to the discrete nature of electron states using midinfrared femtosecond spectroscopy. This dynamic saturation is a consequence of the gradual filling of the discrete quantum-dot electron states due to the capture of electrons injected in the barrier. Our interpretation of the differential transmission experiments is confirmed by a comparison with a rate-equation model with the capture and intersublevel relaxation time as fit parameters yielding 10 ps and 1 ps, respectively. We discuss the mechanism responsible for these relaxation times.