Recombination dynamics of localized excitons in a CdSe/ZnSe/ZnSxSe1

Optical properties of localized excitons have been studied in a highly strained CdSe quantum well with 1-ML thickness by employing time-resolved photoluminescence (PL) and nonlinear PL spectroscopy under various excitation conditions. At 20 K, the time-integrated PL from the well layer was peaked at 2.7276 eV with a linewidth of 21 meV under low excitation intensity (0.11 μJ/cm2). The lifetime ranged from 200 ps to 50 ps as the monitored photon energy was changed from the low-energy tail to the high-energy one. The behavior could be well understood as a result of exciton localization, which is induced by terraces and islands with units of ML thickness fluctuation lying at the interface between CdSe and ZnSe. An emission with the fast decay component was observed at the low-energy side of the peak (2.7168 eV) under higher excitation condition. The emission could be well resolved as a positive component by the nonlinear PL measurement, and originates from the many-body effect of localized excitons, which is probably attributed to localized biexcitons