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The photoluminescence(PL)spectra of self-assembled InAs/GaAs quantum dots(QDs)with InAlAs/InGaAs combination cap layer grown by molecular beam epitaxy are studied under different excitation conditions.The intrinsic optical properties of InAs QDs are investigated under resonant excitation condition.A longitudinal optical(LO)phononassisted peak can be well resolved under Eex＜EgGaAs,which give evidence that the phonon-related process is dominated for carrier relaxation in InAs QDs with InAlAs/InGaAs combination cap layer when they are under resonant excitation condition.A rate equation model is established to interpret the difference of thermal activation energy(Ea).The Ea measured under Eex＜EgGaAs,can exactly describe the intrinsic physical mechanism of temperature-induced quenching in InAs QDs,because it can be irrespective of the barrier materials.This result will benefit to validating the parameters of quantum dots infrared photodetector(QDIP)in sequent procedure of device fabrication.