Carrier relaxation processes in magnetic semiconductor quantum-dot systems

The energy relaxation process of CdSe/ZnMnSe quantum dots (QDs) was investigated using polarization-selective magneto-photoluminescence (PL). Peaks from the Mn ²⁺ internal transition, the CdSe QDs, and the ZnMnSe barrier were observed in the system. The CdSe QD peak was relatively weak while the intensity of the Mn ²⁺ transition was strong in the spectrum taken at zero magnetic field. However, the peaks intensities changed significantly when a magnetic field was applied, and the situation became reversed (i.e., the CdSe QD peak become stronger than the peak due to the Mn ²⁺ internal transition, specifically for σ ⁺ polarization). The opposite intensity behavior was observed in the peak from the Mn ²⁺ ions and in the PL of the CdSe QDs and revealed that these two carrier capture centers competed with each other for carriers excited in the ZnMnSe barrier. The variation in the Mn ²⁺ internal transition with the magnetic field was well described by using a model developed under an angular momentum selection rule. This suggests that competition between the two energy transfer processes in the CdSe/ZnMnSe QD system is responsible for the observed PL intensity behavior.