  We consider the charged exciton complexes of an ideal two-dimensional
electron-hole system in the limit of strong magnetic fields. A series of
charged multiple-exciton states is identified and variational and finite-size
exact diagonalization calculations are used to estimate their binding energies.
We find that, because of a hidden symmetry, bound states of excitons and an
additional electron cannot be created by direct optical absorption and, once
created, have an infinite optical recombination lifetime. We also estimate the
optical recombination rates when electron and hole layers are displaced and the
hidden symmetry is violated.
