Photoluminescence comparation of InAs quantum dots with different capping

We have studied the effect of different cap layers on optical property of InAs quantum dots (QDs) on GaAs (100) substrate. Temperature dependent photoluminescence (PL) indicates that the PL integrated Zn intensity from the ground state of InAs QDs capped with an intermediate InAlAs/InGaAs combined layer drops very little as compared to QDs capped with a thin InGaAs or GaAs layer from 15 K up to room temperature. PL integrated intensity ratio of the first excited to ground states for InAs QDs capped with an intermediate InAlAs/InGaAs layer is unexpectedly decreased with increasing temperature, which we tentatively attribute to phonon bottleneck effect.