Inter-island transport in CdSe/ZnSe quantum heterostructures

We report on localization dynamics of excitons in ensembles of self-organized CdSe islands embedded in ZnSe. The experimental methods employed are temperature-dependent, spatially resolved photoluminescence (mu-PL), spatially integrated PL (macro-PL), as well as time-resolved PL (TRPL). We observe the well known non-monotonous shift of the PL maximum with temperature caused by redistribution of the excitons amongst the islands. The measured shift is compared with the exact shift of the bandgap deduced from mu-PL measurements and found to depend strongly on island size and distribution. These transport processes are recovered in the temporal evolution of the PL. The decaytime of the spectrally integrated PL reaches its maximum at exactly the same temperature at which the redhift of the macro-PL turns into a blueshift. In TRPL the PL-spectrum. consists of two contributions. We put the emission on the high energy side down to excited states in the islands.