Repulsive exciton-exciton interaction in quantum dots

Biexcitons localized in single InAs/GaAs quantum dots (QD's) are investigated by cathodoluminescence, demonstrating an anticorrelation of the biexciton binding energy and the exciton transition energy. The binding energy decreases with increasing transition energy changing its sign at about 1.24 eV. The "binding" to "antibinding" transition is attributed to three-dimensional confinement, quenching correlation, and exchange and causing local charge separation. Model calculations of the biexciton in truncated InAs/GaAs QD's demonstrate the observed trend to result from the decreasing number of localized excited states with decreasing QD size. The interaction with resonant states in the wetting layer is found to be negligible.