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 gas in a high-magnetic field is presented. In contrast to previous calculations, three bound X- stares (one singlet and two triplets) are found in a narrow and symmetric GaAs quantum well. The singlet and a ''bright" triplet are the two optically active states observed in experiments. The bright triplet 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 the short-range character of the e-X- interactions effectively isolates bound 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 decrease of the oscillator strength of the dark triplet X- as a function of nu(-1).