COULOMB EFFECTS IN SPATIALLY SEPARATED ELECTRON AND HOLE LAYERS IN COUPLED QUANTUM WELLS
Butov L.V., Imamoglu A., Compman K.L., Gossard A.C.

Received: June 7, 2000

PACS: 71.35.-y

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We report on the (magneto-) optical study of many-body effects in spatially separated electron and hole layers in GaAs/Al_xGa_1-xAs coupled quantum wells (CQWs) at low temperatures (T=1.4 K) for a broad range of electron-hole densities. Coulomb effects were found to result in an enhancement of the indirect (interwell) photoluminescence (PL) energy with increasing the electron-hole density both for zero magnetic field and at high fields for all Landau level transitions; this is in contrast to the electron-hole systems in single quantum wells (QWs) where the main features are explained by the band gap renormalization 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 space condensation to droplets is energetically unfavorable. At high densities of separated electrons and holes, a new direct (intrawell) PL line has been observed: its relative intensity increased both in PL and in absorption (measured by indirect PL excitation) with increasing density; its energy separation from the direct exciton line fits well to the X^- and X⁺ binding energies previously measured in single QWs. The line is therefore attributed to direct multiparticle complexes.