Thermal activation and phase relaxation of excitons in CdSe/ZnSSe quantum island structures

The thermal activation and dephasing of excitons in self-organized CdSe/ZnS Se quantum islands grown by metalorganic vapour phase epitaxy is investigat ed using temperature dependent photoluminescence (PL) and spectrally resolv ed four-wave mixing (FWM). At low temperatures a multi exponential decay of the photon echo is observed indicating the presence of exciton states with different localization at comparable transition energies. With rising temp erature the localized excitons are activated into more delocalized states l eading to a blueshift of the PL maximum and an increasingly mono-exponentia l decay of the FWM signal. From the: biexciton-induced transition a biexcit on binding energy of 11.5 meV is determined.