Polarized magnetophotoluminescence (MPL) measurements on a high-mobility $\delta$-doped $\mathrm{GaAs}/{\mathrm{Al}}_{0.55}{\mathrm{Ga}}_{0.45}\mathrm{As}$ single quantum well from 0 to 60 T at temperatures between 0.37 and 2.1 K are reported. In addition to the neutral heavy-hole magnetoexciton ${(X}^0),$ the singlet ${(X}_s^{-})$ and triplet ${(X}_t^{-})$ states of the negatively charged magnetoexciton are observed in both polarizations. The energy-dispersive and time-resolved MPL data suggest that their development is fundamentally related to the formation of the neutral magnetoexciton. At a magnetic field of 40 T the singlet and the triplet states cross as a result of the role played by the higher Landau levels and higher-energy subbands in their energetic evolution, confirming theoretical predictions. We also observed the formation of two higher-energy peaks. One of them is completely right circularly polarized and its appearance can be considered a result of the electron-hole exchange interaction enhancement with an associated electron g factor of 3.7 times the bulk value. The other peak completely dominates the MPL spectrum at fields around 30 T. Its behavior with magnetic field and temperature indicates that it may be related to previous anomalies observed in the integer and fractional quantum Hall regimes.

• Received 29 June 1999

DOI:https://doi.org/10.1103/PhysRevB.61.4731