Observation of biexcitonic quantum beat in strain-induced GaAs quantum dots

Four-wave mixing in strain-induced GaAs quantum dots formed in a GaAs quantum well is studied using a highly sensitive heterodyne technique. A clear oscillation with a period of 1 ps is observed, recognized as a biexcitonic quantum beat based on its polarization dependence. The period of the beat is about 1.5 times shorter than that from the quantum well in the same sample. The beat represents direct evidence of an increase in the biexciton binding energy in the dots due to lateral confinement potential originating from the stressors.