Reduced carrier trapping in CdSe/ZnS/CdSe heterostructure quantum dots inferred from temperature dependent spectral studies

Abstract

We report temperature dependent photoluminescence (TDPL) characteristics of CdSe/ZnS core-shell and coupled 0D-2D CdSe/ZnS/CdSe heterostructure quantum dots (HQDs). Anomalous, behavior of temperature dependent PL linewidth seen in core-shell HQDs is ascribed to the relaxation of carriers into interfacial strain related local energy minimum. TDPL characteristics show largest exciton-acoustic phonon and exciton-LO phonon coupling in core-shell HQDs compared to other QDs. These are caused by enhanced deformation potential interaction and enhanced Fröhlich interaction due to the interfacial strain field. Further, relatively lower strength of exciton-acoustic phonon coupling in 0D-2D HQDs is due to relaxation of interfacial strain. Temperature dependence of spectrally integrated PL intensity shows nonradiative relaxation below 150 K due to thermal activation of carriers in surface tarp states while at temperatures above, it is dominated by carrier thermal escape mediated by exciton-LO phonon interaction involving lesser number of phonons in 0D-2D HQDs.