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We report observation of positively charged excitons (X^+) in GaAs quantum wells remotely doped with acceptors. Upon reducing the excess hole density, by photoexciting carriers in the doped barrier layer, we observe the neutral excitonic transition strengthen relative to X^+. Further confirmation of the X^+ assignment is provided by its temperature and magnetic-field dependence. We observe both the antisymmetric (singlet) and symmetric (triplet) X^+ spin states.
Shields et al. (Tue,) studied this question.