Efficient room temperature carrier trapping in quantum dots by tailoring the wetting layer

The temperature dependence of carrier confinement in states of self-assembled ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{As}$ quantum dots (QDs) embedded in ${\mathrm{Al}}_y{\mathrm{Ga}}_{\text{1−y}}\mathrm{As}$ barriers has been investigated by means of photoluminescence (PL) measurements. We show that photoexcited carriers above the AlGaAs barriers have two recombination channels that contribute to the temperature quenching of the PL from QDs: (a) carrier losses in the AlGaAs layers during the relaxation process and (b) thermal evaporation of captured carriers out of QDs. The interplay between these two mechanisms determines the behavior of the nonresonantly excited photoluminescence as a function of temperature. Eliminating the first contribution by using resonant excitation of the QD PL, we demonstrate a definite enhancement of the carrier confinement at room temperature in InGaAs/AlGaAs QDs by increasing the Al content. We show that this effect is related to the increase in the energy separation between the electronic states in the QD and the wetting layer.