EXCITON TRIONS IN II-VI HETEROSTRUCTURES

Optical spectra associated with transitions that create or annihilate charged excitons X- or X+ can be observed in quantum well heterostruct ures containing an electron gas or a hole gas, respectively. A review is given of properties of trion states in CdTe quantum wells in zero f ield and of the magnetic field-dependence of the circular polarization and oscillator strength of the trion optical resonance. The possibili ty that disorder is needed to stabilise trion states in concentrated 2 D electron or hole systems is discussed. PACS numbers: 73.20.Dx, 78.66 .Hf, 71.35.Ji, 78.20.Ls.