Charged many-particle complexes: Properties of an indirect trion

A system of spatially separated interacting excitons and electrons is considered. The formation of a spatially indirect trion in this system is investigated. The asymptotic behavior of the binding energy of this charged many-particle complex is determined in the limits of large and small layer separations. The variation of the binding energy due to screening by the 2D electron gas is calculated. The bound state of the spatially separated exciton and electron is shown to disappear from the collective excitation spectrum at a certain threshold concentration of 2D electrons.