Two-photon absorption of biexcitons in ZnS-based quantum wells

Two-photon absorption processes of biexcitons in ZnS-based quantum-well structures have been studied by means of photoluminescence excitation spectroscopy. The peak position of two-photon absorption of biexcitons was dependent on the detected energy position in the photoluminescence excitation measurement. The energy difference between the one-photon exciton resonance and the two-photon biexciton resonance increased as the detected energy position was moved towards the lower-energy side of the biexciton luminescence. This result indicated the biexciton localization and the resultant increase in the biexciton binding energy.