Spectral engineering of carrier dynamics in In(Ga)As self-assembled quantum dots

Time-resolved photoluminescence upconversion with 200 fs resolution is used to investigate the carrier capture, energy relaxation, and radiative recombination in two self-assembled quantum-dot ensembles with distinctly different sizes and energy spectra. When carriers are excited into the wetting layer at low density and low lattice temperature, the relaxation time to the ground state of the larger dots is ∼1 ps, but the corresponding time for the smaller dots with larger energy spacings is ∼7 ps. This, along with the observed temperature dependence, suggests phonon participation in the relaxation process. At low temperatures, the radiative recombination time in the smaller dots is approximately twice that of the larger dots. The reduced oscillator strength in the smaller dots may be due to a reduced electron–hole wave-function overlap in the smaller dots, in addition to a size-dependent super-radiance effect.