Effects of thermal emission and re-trapping of photo-injected carriers on the optical transitions of InAs/GaAs quantum dots

Photoluminescence (PL) measurements are presented for self-assembled InAs/GaAs quantum dots (QDs). Under a very low excitation density, the 8K-PL spectrum of the QD sample shows two well-defined sub-bands. The PL subbands are clarified as emissions from the ground state (GS) and the first excited state (FES) of the dots. Different from that of the FES transition, a sigmoidal temperature-dependent variation is observed from the integrated PL intensity (IPLI) of the GS transition. This behavior is related to the carrier exchange between the excited states and the GS of the dots. A simple rate equation model, which takes into account the effects of the thermal escape and re-trapping of photo-injected carriers, is proposed to describe the sigmoidal variation of the IPLI. A good agreement between the model simulation and the experimental results is obtained and therefore supports the argument for the carrier exchange between the excited states and the ground states.