Photoluminescence of negatively charged excitons in high magnetic fields

We have studied the low-temperature photoluminescence of the two-dimensiona l electron gas in a single GaAs quantum well in magnetic fields up to 50 T over four orders of magnitude of illumination intensity. At the very highes t illumination powers, where the recombination is excitonic at zero field, we find that the binding energy of both the singlet and triplet states of t he negatively charged exciton (X-) increase monotonically with the applied field above 15 T. This contradicts recent calculations for X-, but is in ag reement with adapted calculations for the binding energy of negative-donor centers. At low-laser powers we observe a strong transfer of luminescence i ntensity from the singlet (ground) state to the tripler (excited) state as the temperature is reduced below 1 K. This is attributed to the spin polari zation of the two-dimensional electron gas by the applied magnetic field. [ S0163-1829(99)01104-2].