MANY-ELECTRON EXCITONS AND FERMI-EDGE SINGULARITIES IN WIDE, PARABOLIC (AL,GA)AS QUANTUM-WELLS

Wide n-type parabolic (Al,Ga)As quantum wells have been studied by use of magneto-optical techniques. Striking spectral features, reflective of many-electron-one-hole exciton effects, have been observed in these systems. These effects involve the Fermi-edge singularity phenomenon, now in a quasi-three-dimensional case. In this system, the closely spaced conduction subbands act as resonating channels for multiple electron-hole Coulomb scattering, allowing the singularity enhancement to influence the entire (shallow) Fermi sea. The photoluminescence spectra show pronounced enhancements at high energy (near E(F)) in addition to prominent subband exciton peaks despite the presence of an electron Fermi sea. Applied magnetic fields show subband depopulation effects as well as strong, periodic enhancements whenever the Fermi level is in near resonance with a higher subband.