Mechanisms of Manganese-Assisted Nonradiative Recombination in Cd(Mn)Se/Zn(Mn)Se Quantum Dots

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Mechanisms of nonradiative recombination of electron-hole complexes in Cd(Mn)Se/Zn(Mn)Se quantum dots accompanied by interconfigurational excitations of Mn²⁺ ions are analyzed within the framework of single electron model of deep 3d-levels in semiconductors. In addition to the mechanisms caused by Coulomb and exchange interactions, which are related because of the Pauli principle, another mechanism due to sp-d mixing is considered. It is shown that the Coulomb mechanism reduces to long-range dipole-dipole energy transfer from photoexcited quantum dots to Mn²⁺ ions. The recombination due to the Coulomb mechanism is allowed for any states of Mn²⁺ ions and e-h complexes. In contrast, short-range exchange and sp-d recombinations are subject to spin selection rules, which are the result of strong lh-hh splitting of hole states in quantum dots. Estimates show that efficiency of the sp-d mechanism can considerably exceed that of the Coulomb mechanism. The phonon-assisted recombination and processes involving upper excited states of Mn²⁺ ions are studied. The increase in PL intensity of an ensemble of quantum dots in a magnetic field perpendicular to the sample growth plane observed earlier is analyzed as a possible manifestation of the spin-dependent recombination.