Comparative study of Photoluminescence variation in InAs Quantum dots embedded in InAlGaAs Quantum wells
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Comparative study of Photoluminescence variation in InAs Quantum dots embedded in InAlGaAs Quantum wells J.L. Casas Espinola1, T.V. Torchynska1, L. D. Cruz. Diosdado2 and G. Polupan3 ESFM– Instituto Politécnico Nacional, México D. F. 07738, México 2 UPIITA– Instituto Politécnico Nacional, México D. F. 07720, México 3 ESIME– Instituto Politécnico Nacional, México D. F. 07738, México
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ABSTRACT The photoluminescence (PL) and its temperature dependences have been studied in MBE grown InAs quantum dots (QDs) embedded in Al0.3Ga0.7As/In0.15Ga0.85As/AlxGa1-xInyAs quantum wells (QWs) in dependence on the composition of capping layers. Two types of capping layers (Al0.3Ga0.7As andAl0.40Ga0.45In0.15As) were investigated. Temperature dependences of PL peak positions in QDs have been analyzed in the range of 10-300K and 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 between QDs and capping layers in dependence on the capping layer compositions. The band gap fitting parameters obtained for InAs QDs have been compared with known ones for the bulk InAs crystal. It is shown that the efficiency of the Ga(Al)/In inter diffusion is high in the QD structures with Al0.3Ga0.7As capping layer. Finally the reasons of higher thermal stability of the structure with Al0.40 Ga0.45 In 0.15 As capping layer have been analyzed and discussed. INTRODUCTION Over the past twenty years, zero-dimensional (0D) quantum dot (QD) systems with threedimensional quantum confinement have attracted considerable interest from both the fundamental physics and potential device applications in: light – emitting and photo diodes, solar cells and memory devices [1-3]. The realization of the efficient light-emitting devices operated at room temperature requires understanding the QD PL temperature dependences and the study of the reasons of PL variation versus temperature. The PL intensity decay in InAs QDs, as a rule, is attributed to thermal escape of excitons from the QDs into a wetting layer (WL) or into the GaAs barrier [4-8], or to a thermally activated capture of excitons by the nonradiative defects in the GaAs barrier or at the GaAs/InAs interface [5, 8]. It was shown experimentally that the main reason for the PL thermal decay in QD structures is related to the thermal escape of the excitons or correlated electron-hole pairs from QDs [8-10]. In QD structures introducing the additional intermediate AlxGa1-xAs layers into InGaAs/GaAs QWs will increase the height of the potential barrier for the exciton thermal escape from QDs into the barrier and can permit the application of these QD structures at higher temperatures. The same effect can be achieved with the introduction of the intermediate AlxGa1xInyAs QW layers in InGaAs/GaAs QWs. It is known that QD lasers fabricated with AlInGaAs QWs have shown superior performances at a higher temperature due to a larger conduction band offset [11, 12]. Even though the better device performance of QD
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