Emission and X ray diffraction in AlGaAs/ InGaAs Quantum wells with embedded InAs Quantum dots
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Emission and X ray diffraction in AlGaAs/ InGaAs Quantum wells with embedded InAs Quantum dots R. Cisneros Tamayo1, I.J. Gerrero Moreno1, A. Vivas Hernandez1, J.L. Casas Espinola2 and L. Shcherbyna3 1
ESIME– Instituto Politécnico Nacional, México D. F. 07738, México ESFM– Instituto Politécnico Nacional, México D. F. 07738, México 3 V. Lashkaryov Institute of Semiconductor Physics at NASU, Kiev, Ukraine 2
ABSTRACT The photoluminescence (PL), its temperature dependence and X-ray diffraction (XRD) have been studied in MBE grown GaAs/AlGaAs/InGaAs/AlGaAs /GaAs quantum wells (QWs) with InAs quantum dots embedded in the center of InGaAs layer in the freshly prepared states and after the thermal treatments during 2 hours at 640 or 710 oC. The structures contained two buffer (Al0.3Ga0.7As/In0.15Ga0.85As) and two capping (In0.15Ga0.85As / Al0.3Ga0.7As) layers. The temperature dependences of PL peak positions have been analyzed in the temperature range 10500K with the aim to investigate the QD composition and its variation at thermal annealing. The experimental parameters of the temperature variation of PL peak position in the InAs QDs have been compared with the known one for the bulk InAs crystals and the QD composition variation due to Ga/Al/In inter diffusion at thermal treatments has been detected. XRD have been studied with the aim to estimate the capping/buffer layer compositions in the different QW layers in freshly prepared state and after the thermal annealing. The obtained emission and XRD data and their dependences on the thermal treatment have been analyzed and discussed. INTRODUCTION Self-assembled InGaAs/GaAs quantum dots (QDs) are especially attractive for the application in lasers, photodiodes and memory devices [1-4]. The realization of efficient lightemitting devices operated at room temperature requires understanding the QD PL temperature dependences and the study of the reasons of PL 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 [5-11], or to a thermally activated capture of excitons by the nonradiative defects in the GaAs barrier or at the GaAs/InAs interface [5, 8, 9]. It was shown experimentally that the main reason for the PL thermal decay in QD structures related to the thermal escape of the excitons, or correlated electron-hole pairs, from QDs [10 15]. In QD structures introducing the additional AlxGayAs layers into InGaAs/GaAs quantum wells ( QWs) will, as it is expected, to increase the height of potential barrier for the exciton thermal escape from QDs into the barrier and can permit the application of these QD structures at higher temperatures. Improved understanding of the operation and the design peculiarities of InAs QDs embedded into InGaAs/AlGaAs QWs could be obtained from the study of the variation of PL spectra and XRD pattern at thermal annealing. EXPERIMENTAL DETAILS
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The solid-source molecular beam epitaxy (MBE) in V80H reactor was used to gro
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