We investigate the lateral transport of excitons in ZnSe quantum wells by using time-resolved micro-photoluminescence enhanced by the introduction of a solid immersion lens. The spatial and temporal resolutions are 200 nm and 5 ps, respectively. Strong deviation from classical diffusion is observed up to 400 ps. This feature is attributed to the hot-exciton effects, consistent with previous experiments under cw excitation. The coupled transport-relaxation process of hot excitons is modelled by Monte Carlo simulation. We prove that two basic assumptions typically accepted in photoluminescence investigations on excitonic transport, namely (i) the classical diffusion model as well as (ii) the equivalence between the temporal and spatial evolution of the exciton population and of the measured photoluminescence, are not valid for low-temperature experiments.

We demonstrate the combination of a hemispherical solid immersion lens with a microphotoluminescence set-up. Two advantages introduced by the SIL, an improved resolution of 0.4 times the wavelength in vacuum and a 5 times enhancement of the collection efficiency, make it an ideal system for spatially resolved spectroscopy applications. The influence of the air gap between the SIL and the sample surface is investigated in detail. We confirm the tolerance of the set-up to an air gap of several micrometers. Such a system is proven to be ideal system in the studies of exciton transport and polarization dependent single quantum dot spectroscopy.

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 (m-PL), spatially-integrated PL (macro-PL), as well as time-resolved PL (TRPL). We see the often observed non-monotonous shift of the PL maximum with temperature which we can explain by a redistribution of the excitons amongst the islands. The measured shift is compared with the exact shift of the bandgap deduced from m-PL measurements and is found to depend strongly on island size and distribution. These transport processes are recovered in the temporal evolution of the PL. The decay time of the spectrally integrated PL reaches its maximum at exactly the same temperature at which the redshift of the macro-PL turns into a blueshift.

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