Charged excitons in a dilute two-dimensional electron gas in a high magnetic field

A theory of charged excitons X- in a dilute two-dimensional (2D) electron g as in a high-magnetic field is presented. In contrast to previous calculati ons, three bound X- stares (one singlet and two triplets) are found in a na rrow and symmetric GaAs quantum well. The singlet and a ''bright" triplet a re the two optically active states observed in experiments. The bright trip let has the binding energy of about 1 meV, smaller than the singlet and a " dark'' triplet. The interaction of bound X-'s with a dilute 2D electron gas is investigated using exact diagonalization techniques. It is found that t he short-range character of the e-X- interactions effectively isolates boun d X- states from a dilute e-h-plasma. This results in the insensitivity of the photoluminescence spectrum to the filling factor nu, and a rapid decrea se of the oscillator strength of the dark triplet X- as a function of nu(-1 ).