Direct and spatially indirect excitons in GaAs/AlGaAs superlattices in strong magnetic fields

Abstract

Luminescence and luminescence excitation spectra are used to study the energy spectrum and binding energies of direct and spatially indirect excitons in GaAs/AlGaAs superlattices having different electron and hole miniband widths in high magnetic fields perpendicular to the heterolayers. The ground state of the indirect excitons formed by electrons and holes which are spatially distributed among neighboring quantum wells is found to lie between the ground 1s state of the direct excitons and the threshold of the continuum of dissociated exciton states in the minibands. The indirect excitons have a substantial oscillator strength when the binding energy of the exciton exceeds the scale of the width of the resulting miniband. It is shown that a high magnetic field shifts a system of symmetrically bound quantum wells toward weaker bonding. At high exciton concentrations, spatially indirect excitons are converted into direct excitons through exciton-exciton collisions.