SPIN POLARIZATION IN SEMIMAGNETIC <font>CdMnSe/ZnSe</font> QUANTUM DOTS WITH ZERO EXCITON g FACTOR

We have investigated the degree of circular polarization (ρ) in the emission of semimagnetic CdMnSe/ZnSe quantum dots (QDs) with Mn contents of nominally 0, 1 and 2 %. Circularly polarized excitation was used to control the polarization of the excited carriers. The g factors were determined from the dependence of ρ on the magnetic field strength. We demonstrate that in QDs with 1 % Mn the exciton g factor is vanishingly small. We also present measurements on the excitation power dependent changes of the polarization. A direct heating mechanism is identified as origin of the drastic enhancement of the g factor by ramping up the excitation power. For high laser powers the exciton g factor increases by a factor of 30. In addition, by comparing the luminescence polarization of QDs with 2 % Mn and without Mn a sign reversal of the g factor was observed.