Excitons and deexcitons in a neutral two-dimensional magnetoplasma with a strong population inversion

Magnetoabsorption and emission by charge carriers in quantum wells under the conditions of a strong population inversion is investigated. The magnetoplasma is assumed to be neutral, the filling factor to be integer for both electrons and holes, and the temperature T=0. It is shown that under these conditions there exist two types of elementary excitations: excitons and deexcitons. The latter consist of a Fermi hole in the conduction band and an electron on an empty level in the valence band. The quasimomentum may be ascribed to deexcitons just as for excitons but the energy of the deexcitons is negative. It is shown that both excitons and deexcitons are stable near the direct Burstein edge (stability path), and a relation between their energies is found. Existence of deexcitons ensures the presence of narrow bands in the emission spectra due to final-state Coulomb interactions.