High magnetic field studies of charged exciton localization in GaAs/Al_xGa_1−xAs quantum wells

We report on low temperature, polarization resolved, high magnetic field (up to 23 T) photoluminescence experiments on high mobility asymmetric GaAs quantum wells. At high magnetic fields, we detect two strong emission lines of the neutral and positively charged excitons (X and X⁺) and a series of weaker lines of the excitons bound to ionized acceptors (AX⁻). From polarization energy splittings of these lines, we determine the hole Landé factors (g_h) of different complexes. For X and X⁺, g_h initially grows with magnetic field and then saturates at g_h = 0.88 and 1.55, respectively; for AX⁻'s, g_h begins from a high value (from 6 to 11 at zero field) and decreases with the field growth. This contrasting behavior is traced to the structure of valence band Landau levels, calculated numerically in the Luttinger model, beyond axial approximation. This points to the coexistence (in the same well) of mobile X and X⁺ with localized and interface-pressed AX⁻ states.