Correlation between exciton decay time and Stokes shift in digital magnetic heterostructures

Abstract

The exciton recombination time and the exciton photoluminescence Stokes shift are systematically investigated in a set of CdTe/Cd 1 - x Mg x Te quantum-well samples containing MnTe layers with the thickness below or equal to 1 ML. Similar to diluted magnetic semiconductors, these digital magnetic heterostructures exhibit strongly magnetic-field-dependent photoluminescence lines which are inhomogeneously broadened. Both quantities under investigation depend on the Mn content, on the details of the Mn distribution within the quantum wells, and on the energy of detection. Three sets of samples are investigated: digital magnetic heterostructures containing four MnTe layers with equidistant spacing and various thickness of the MnTe layers, quantum wells containing 1-ML MnTe at various positions in the quantum well, and quantum wells containing in total 1-ML MnTe but distributed in the quantum well in different ways. For all samples, the exciton recombination time is strongly correlated to the Stokes shift. This correlation is caused by exciton localization, leading to a mixing of radiatively decaying states with small momentum with nonradiative states with large momentum. In our experiment, however, a linear dependence between the exciton decay time and the Stokes shift is observed, which is not yet explained by theory, to our knowledge. Although, the luminescence properties in semimagnetic semiconductors are affected by exchange interactions leading to the formation of magnetic polarons, this process can be ruled out as the origin of the observed correlation.