Copper Doping of Low-Dimensional Se-Based Semiconductor Structures Grown by Molecular Beam Epitaxy

Copper-doped self-assembled CdSe/ZnSe quantum dots (QDs) and (Zn,Cd)Se/ZnSe quantum wells (QWs) are grown by molecular beam epitaxy. Low-temperature luminescence properties of these structures are investigated in detail including circular polarization-resolved magneto-photoluminescence and time-resolved spectroscopy. A significant spectral shift of excitonic emission from both kinds of low-dimensional structures is observed as a result of copper doping. It is found that the excitonic emission energy of copper-doped CdSe QDs may vary even by 200 meV, depending on the copper molar fraction. Apart from the excitonic emission, a characteristic optical transition related to the recombination of conduction-band electrons with holes strongly localized on copper ions is identified and it appears about 0.8 eV below the excitonic emission. Magneto-luminescence measurements reveal that circular polarization of this copper-related emission is significantly stronger than the circular polarization of the excitonic emission. Possible explanations of this effect are discussed including different g-factor values expected for spin-split sublevels, as well as charge-carrier dynamics present in these two optical transitions.