FERMI-EDGE SINGULARITIES IN DOPED QUANTUM WIRES AND QUANTUM-WELLS

The optical properties of quantum wires and quantum wells are investigated. We are concerned with the effects produced by the localization of electrons and holes either in the same (direct transitions) or different space regions (indirect transitions). The emission and absorption spectra are obtained by solving an effective Bethe-Salpeter equation including a static screened Coulomb interaction. Fermi Edge Singularities (FES) are obtained and their dependence on temperature and density of carriers are analyzed. In order to obtain strong FES, it is necessary that two special points are fulfilled: (i) the hole mass goes to infinity; and (ii) a spatial symmetry breaking of the system (spatially indirect transitions). When the latter condition is satisfied and the bottom of the second conduction subband approaches the first one, a new channel of scattering is favoured and the spectra show a large enhancement at the Fermi level. We compare our results with the experimental situations.