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 recom bination in two self-assembled quantum-dot ensembles with distinctly differ ent sizes and energy spectra. When carriers are excited into the wetting la yer at low density and low lattice temperature, the relaxation time to the ground state of the larger dots is similar to1 ps, but the corresponding ti me for the smaller dots with larger energy spacings is similar to7 ps. This , along with the observed temperature dependence, suggests phonon participa tion in the relaxation process. At low temperatures, the radiative recombin ation time in the smaller dots is approximately twice that of the larger do ts. The reduced oscillator strength in the smaller dots may be due to a red uced electron-hole wave-function overlap in the smaller dots, in addition t o a size-dependent super-radiance effect. (C) 2001 American Institute of Ph ysics.