Negatively charged trion in ZnSe single quantum wells with very low electron densities

The polarization- and excitation-intensity-dependent photoluminescence of the negatively charged trion is investigated for ZnSe single quantum wells embedded in ternary and quaternary barriers. The measurements were performed in magnetic fields up to 11.8 T perpendicular to the quantum well. The spin-singlet state of the trion is clearly identified. In contrast to GaAs quantum wells, the increase of the trion binding energy through the magnetic field is found to be negligible, which is explained by the relatively small spatial extent of the trionic wave function in wide-band-gap materials. For magnetic fields beyond 7 T a resonance becomes stabilized that is identified as excited trion spin-triplet state because of its anticorrelation with the trion spin-singlet state behavior for increasing excitation energy.