Biexciton formation induced by bright-dark exciton transitions in a diluted magnetic semiconductor asymmetric quantum well

We have investigated excitonic states in a (Cd,Mg)Te/CdTe/(Cd,Mn)Te asymmetric quantum well, during the photoluminescence decay processes. The intensity ratio of biexciton to exciton showed almost a linear dependence. The biexciton luminescence showed a longer decay time when compared with that of the exciton. The rate equations based on our model taking account of the dark exciton level (J=±2) were used to analyze this anomalous exciton-biexciton system. Our analysis leads to a conclusion that the new channel from a dark exciton has an essential role when biexcitons are created in II-VI diluted magnetic semiconductor quantum wells.