HR XRD and Emission of In x Ga 1-x As/GaAs quantum wells with embedded InAs quantum dots at the variation of In x Ga 1-x
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HR XRD and Emission of InxGa1-xAs/GaAs quantum wells with embedded InAs quantum dots at the variation of InxGa1-xAs composition Leonardo G. Vega Macotela, Ricardo Cisneros Tamayo and Georgiy Polupan ESIME– Instituto Politécnico Nacional, México D. F. 07738, México. ABSTRACT The high resolution X ray diffraction (HR-XRD) diagrams have been studied in the GaAs /InxGa1-xAs /In0.15Ga0.85As/GaAs quantum wells with embedded InAs quantum dots (QDs) in dependence on the composition of the capping InxGa1-xAs layers. The parameter x in capping InxGa1-xAs layers varied from the range 0.10-0.25. These technological changes have been accompanied by the variation non-monotonously of InAs QD emission. Numerical simulation of HR-XRD results has shown that the level of elastic strains and the composition of quantum layers vary none monotonously in studied QD structures. Simultaneously it was revealed that the process of Ga/In inter diffusion at the InxGa1-xAs/InAs QD interface are characterized by the dependence non monotonous versus parameter x in capping InxGa1-xAs layers. The physical reasons of the mentioned optical and structural effects in studied structures have been discussed. INTRODUCTION In the past twenty years, zero-dimensional quantum dot (QDs) systems with threedimensional quantum confinement have attracted considerable attention owing to the fundamental and application reasons [1-3]. The most studded subject is the self-assembled (SA) semiconductor QDs formed by the Stranski–Krastanov (SK) growth mode. The InAs/GaAs QDs have been used as an effective active medium for the optoelectronic devices such as lasers and light emitting diodes, infrared photo-detectors and solar cells [4,5]. It was shown earlier that the InAs QD density can be enlarged significantly if the dots growth on the surface of InxGa1-xAs buffer layer within InxGa1-xAs/GaAs QWs [6]. In these structures photoluminescence (PL) has been enhanced due to the better crystal quality of layers surrounding QDs [7-9] and owing the more effective exciton capture into QWs and QDs [10-14]. It was revealed as well that the emission intensity and PL peak positions vary versus InGaAs layer composition none monotonously [7]. In this paper we try to understand the physical reasons of the emission variation non-monotonously in InAs QD structures with the different In composition in capping InxGa1-xAs layers. EXPERIMENTAL CONDITIONS The experimental set of QD structures was created using the molecular beam epitaxial growth on the (100) oriented 2’’diameter semi-insulating GaAs substrates. Each structure included a 300 nm GaAs buffer layer and a 70 nm GaAs upper capping layer. Between GaAs layers where located three self-organized InAs QD arrays (formed by depositing 2.4 ML of InAs at 490 oC) embedded into an external asymmetric InxGa1-xAs/In0.15Ga0.85As/GaAs QWs separated by the GaAs spacer layers of 30 nm. The InAs QDs in all investigated structures were grown on a buffer layer of 1 nm with the composition In0.15Ga0.85 As under the InAs wetting layer (WL).
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