Effect of Subband Coupling on Exciton Binding Energies and Oscillator Strengths in GaAs-Ga 1- x Al x As Quantum Wells

The authors calculate exciton binding energies and oscillator strengths in GaAs-GaAlAs quantum wells, starting from the subband structure which contains valence band mixing. The effect of Coulomb coupling between excitons belonging to different subbands is calculated and is shown to be important: the strongest interaction is with the exciton continuum. Calculated binding energies agree within 1 meV with photoluminescence excitation experiments. It is shown that parity forbidden excitons have zero oscillator strength even when valence band mixing is included. Therefore, some transitions reported in the literature cannot be ground-state excitons, and are reinterpreted here as excitons in excited states.