Photoluminescence variation in InAs Quantum dots embedded in InGaAs/AlGaAs Quantum wells at thermal annealing
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Photoluminescence variation in InAs Quantum dots embedded in InGaAs/AlGaAs Quantum wells at thermal annealing I. J. Guerrero Moreno1, G. Polupan1 and J.L. Casas Espinola2 ESIME– Instituto Politécnico Nacional, México D. F. 07738, México 2 ESFM– Instituto Politécnico Nacional, México D. F. 07738, México 1
ABSTRACT The photoluminescence (PL) and its temperature dependence have been studied in MBE grown InAs quantum dots (QDs) embedded in GaAs/Al0.3Ga0.7As/In0.15Ga0.85As/AlxGa1-xAs/ GaAs quantum wells (QWs) in dependence on the composition of the capping AlxGa1-xAs layers and after the thermal annealing at 640oC during 2 hours. Two types of capping layers (GaAs and Al0.3Ga0.7As) were investigated.It is shown that annealing initiates the shift of PL peak positions into the high energy spectral range and the value of this shift depends on the composition of capping layers. Temperature dependences of PL peak positions in QDs have been analyzed in the range of 10-300K and are compared with the temperature shrinkage of the band gap in the bulk InAs crystal. This permits to investigate the efficiency of the Ga(Al)/In inter diffusion processes in dependence on the capping layer compositions andthermal annealing. Experimental and fitting parameters obtained for the InAs QDs have been compared with known one for the bulk InAs crystal. It is revealed that the efficiency of the Ga(Al)/In inter diffusion depends essentially on the capping layer compositions. INTRODUCTION Self-assembled InAs/GaAs quantum dots (QDs) are the subject of great interest in the last two decades owing to the fundamental and application reasons [1-3]. It was shown that the QD density can be enlarged significantly by growing the dots within InxGa1-xAs/GaAs quantum wells (QWs) [3, 4]. In mentioned QD structures the photoluminescence (PL) has been enhanced due to the better crystal quality of QW layers and owing to the more effective exciton capture into the QWs and QDs [4]. But even for optimal capping/buffer layer compositions the PL of QDs is characterized by essential non homogeneity [5-8]. The realization of efficient light-emitting devices operated at room temperature requires understanding the QD PL temperature dependence and the study of the reasons of PL non homogeneity and its variation at thermal annealing. The PL intensity decay in InAs QDs, as a rule, attributed to thermal escape of excitons from the QDs into a wetting layer (WL) or into the GaAs barrier [9-15]. In QD structures introducing the additional AlxGa1-xAs layers into InGaAs/GaAs QWs, as it is expected, leads to the increase of the height of the potential barrier for the exciton thermal escape from QDs and can permit the application of these QD structures at higher temperatures. Improved understanding the operation and design peculiarities of InAs QDs
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embedded into InGaAs/AlGaAs QWs could be obtained from the study of the variation of the PL spectra at thermal annealing. EXPERIMENT The solid-source molecular beam epitaxy (MBE) in V80H reactor was used to grow the waveguide struc
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