Lasing and dynamics of photoexcited carriers in graded-index separate confinement Zn1−xCdxSe single quantum wells

In this work we investigated the optical properties and lasing in graded-index separate confinement Zn 1-x Cd x Se/ZnSe heterostructures on In 1-x Ga x As (1 0 0) substrate. The carrier dynamics in the confining graded barriers and the single quantum well are investigated by using time-resolved photoluminescence measurements. Our measurements show the filling of quantum well states and depopulation of barrier states in about 25 ps. Moreover, we observed the reduction of the decay time of the photoluminescence as the excitation intensity was varied from below to above the threshold for lasing. Lasing threshold in these structures was found to be reduced by about one order of magnitude with respect to samples without graded-index profile. The threshold for lasing was in the range from 1 to 145 kW/cm 2 when the sample temperature was varied from 10 to 300 K. In short cavities, at temperatures higher than 150 K a transition from the first to the second quantized state was observed.