Coulomb effects in spatially separated electron and hole layers in coupledquantum wells

We report on the (magneto-) optical study of many-body effects in spatially separated electron and hole layers in GaAs/AlxGa1 xAs coupled quantum well s (CQWs) at low temperatures (T = 1.4 K) for a broad range of electron-hole (e-h) densities. Coulomb effects were found to result in an enhancement of the indirect (interwell) photoluminescence (PL) energy with increasing the e-h density both for a zero magnetic field and at high fields for all Land au level transitions; this is in contrast to the electron-hole systems in s ingle QWs where the main features are explained by the band-gap renormaliza tion resulting in a reduction of the PL energy. The observed enhancement of the ground state energy of the system of the spatially separated electron and hole layers with increasing the e-h density indicates that the real spa ce condensation to droplets is energetically unfavorable. At high densities of separated electrons and holes, a new direct (intrawell) PL line has bee n observed: its relative intensity increased both in PL and in absorption ( measured by indirect PL excitation) with increasing density; its energy sep aration from the direct exciton line fits well to the X (-) and X (+) bindi ng energies previously measured in single QWs. The line is therefore attrib uted to direct multiparticle complexes. (C) 2001 MAIK "Nauka/ Interperiodic a".