Influence of copper dopants on the photoluminescence of single CdTe quantum dots

We report on a magnetoluminescence study of epitaxially grown single CdTe quantum dots doped with small amounts of copper (of the order of 0.1 at. %) embedded in a ZnTe semiconducting matrix. The survey of tens of quantum dots did not reveal the presence of a dot containing one Cu ion in a +2 oxidation state with a localized spin 1/2. Instead, more complicated patterns of emission lines were detected. This fact leads us to a conclusion that Cu impurities are in a Cu+ spinless state and are subject to trigonal strain. Such an assumption gives (as our model calculations show) a qualitative agreement with an observed decrease of the excitonic g-factors and the values of the circular polarization degree as compared to those values in CdTe quantum dots without copper impurities. To further improve the agreement, we propose that the quantum dot formation in the Stranski-Krastanov mode is perturbed by the presence of copper, which results in a slight tilt of the dot quantization axis away from the [100] growth direction.