Impact of capping layer type on emission of InAs quantum dots embedded in InGaAs/In_xAl_yGa_zAs/GaAs quantum wells

The optical and structural properties of In_0.15Ga _0.85As/In_xAl_yGa_zAs/GaAs quantum wells with embedded InAs quantum dots (QDs) were investigated by the photoluminescence (PL), its temperature dependence, X-ray diffraction (XRD), and high resolution (HR-XRD) methods in dependence on the composition of capping In_xAl_yGa_zAs layers. Three types of capping layers (Al_0.3Ga_0.7As, Al_0.10Ga _0.75In_0.15As, and Al_0.40Ga _0.45In_0.15As) have been used and their impact on PL parameters has been compared. Temperature dependences of PL peak positions in QDs have been analyzed in the range of 10-500 K and to compare with the temperature shrinkage of band gap in the bulk InAs crystal. This permits to investigate the QD material composition and the efficiency of Ga(Al)/In inter diffusion in dependence on the type of In_xAl_yGa _zAs capping layers. XRD and HR-XRD used to control the composition of quantum well layers. It is shown that QD material composition is closer to InAs in the structure with the Al_0.40Ga_0.45In_0.15As capping layer and for this structure the emission 1.3 μm is detected at 300 K. The thermal decay of the integrated PL intensity has been studied as well. It is revealed the fast 10²-fold thermal decay of the integrated PL intensity in the structure with the Al_0.10Ga_0.75In _0.15As capping layer in comparison with 10-fold decay in other structures. Finally, the reasons of PL spectrum transformation and the mechanism of PL thermal decay for different capping layers have been analyzed and discussed.