Exciton Trions in II-VI Heterostructures

Optical spectra associated with transitions that create or annihilate charged excitons X$\text{}^{-}$ or X$\text{}^{+}$ can be observed in quantum well heterostructures containing an electron gas or a hole gas, respectively. A review is given of properties of trion states in CdTe quantum wells in zero field and of the magnetic field-dependence of the circular polarization and oscillator strength of the trion optical resonance. The possibility that disorder is needed to stabilise trion states in concentrated 2D electron or hole systems is discussed