The influence of size distribution on the luminescence decay from excited states of InAs/GaAs self-assembled quantum dots

We compare the time integrated and time resolved spectra of two samples having coincident ground state emission peaks: one consisting of highly uniform quantum dots, the other grown under conditions which produce a broad distribution of quantum dot sizes. The photoluminescence decay of the ground states in both samples is monoexponential from which we deduce a lifetime of ∼1100 ps independent of excitation power. The excited state decays for the two samples are biexponential with fast and slow components of ∼300 and ∼1100 ps, respectively. These are also independent of excitation power but their contribution to the decay curve changes with power. The data allow us to unequivocally associate the fast component with the excited state decay of larger dots and the slow component with the ground state decay of smaller dots which emit at the same energy. Furthermore, taking into account the degeneracy of the ground state and the optical selection rules for exciton recombination in a confined system we show that the lifetime of the excited state is consistent with the ground state as predicted from Fermi's golden rule.