Bright and dark triplet states of the negatively charged magnetoexcitons revealed in photoluminescence and time-resolved measurements

Continuous and time-resolved magnetophotoluminescence measurements of three GaAs/AlxGa1-xAs heterostructures have been made in high magnetic fields. T he spectra revealed the presence of a singlet and two tripler states (the s o-called "bright" and ''dark'' states) of the negatively charged magnetoexc iton, in addition to the neutral exciton. For an asymmetrically doped singl e quantum well sample, the singlet and the dark triplet states converge (an d possibly cross) at a field of about 40 T. The two single heterojunction s amples on the other hand show no such convergence, and the singlet remains the fundamental state at least in fields to 60 T. The lifetimes of the char ged magnetoexcitons increased linearly with held, whereas the neutral excit on was essentially field independent. The results clarify earlier experimen tal studies, and provide a confirmation of a recent theory of the behavior of charged magnetoexcitons in magnetic fields by Wojs et al.