Recombination dynamics of unthermalised excitons in quantum well structures of II-VI semiconductors

Properties of strongly localised excitons are analysed. In addition, to the known effect of variation of excitons decay time, we show several new phenomena related to the localisation. In particular, we show that potential fluctuations in a quantum well plane can considerably slow down thermalisation of an excess energy of photo-excited excitons and can thus result in radiative decay of unthermalised excitons, We also show that localisation of excitons decreases trapping efficiency of free excitons at donor centres. In consequence, decay time of free excitons emission surprisingly weakly depends on doping level in modulation doped quantum well structures. This is explained by a weak trapping of free excitons by donor impurities, which is inefficient in the quantum well structures with strong potential fluctuations. Bound excitons are preferentially formed in such structures under the excitation, which generates free electrons and holes. We further show that strong localisation effects lead to pronounced Auger-type nonradiative recombination transitions in CdCrTe quantum well structures.