Observation of long-lived excitons in InAs quantum dots under thermal redistribution temperature

We study the temperature-dependent time-resolved photoluminescence (TRPL) of self-assembled InAs quantum dots (QDs). Under low excitation power, a surprisingly long PL decay time is observed at about 60 K, under the thermal redistribution temperature. The long decay time decreases with increasing excitation power but is nearly independent of the detection energy of TRPL measurements. A model considering the spin relaxation through the excited excitonic state is proposed to quantitatively explain the unusual phenomena. The rate equation analysis indicates that the observation of long-lived excitons is caused by the shortened spin-flip time.