The decay time is expected to be determined by the availability of photoexcited holes. The different decay times observed for the QW-related emissions could possibly be due to some spatial distribution in the hole localization potentials, allowing some difference in the corresponding decay times. There is also a possibility that the recombination via the higher electron states is excitonic in character. In this case it would be natural to expect different lifetimes for localized excitons involving different electron states. This greatly facilitates the observation of 2DEG-related PL features, as demonstrated for the first time in this work.
Dynamical studies provide decay times in the sub-ns regime for all emissions observed.
This interpretation is consistent with a simple calculation of the recombination energies in the QW potential. J. S. Im, H. Kollmer, J. Off, A. Sohmer, F. Scholz, A. Hangleiter, Phys. Figure 1 . Growth structure of the modulation doped quantum well sample. Figure 2 .