  Time-resolved photoluminescence measurements show that the decay time for
charged excitons in a GaAs two-dimensional electron gas increases by an order
of magnitude at high magnetic fields. Unlike neutral excitons, the charged
exciton center-of-mass is spatially confined in a ``magnetically-adjustable
quantum dot'' by the cyclotron orbit and the quantum well. The inhibited
recombination is explained by a reduced phase coherence volume of the
magnetically-confined charged excitons.
