Optical And Structural properties of Vertical Aligned Self-Assembled InAs Quantum Dots Multilayers
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Optical And Structural properties of Vertical Aligned Self-Assembled InAs Quantum Dots Multilayers J. C. González, M. I. N. da Silva, W. N. Rodrigues1, F. M. Matinaga1, R. Magalhaes-Paniago1, M. V. Moreira1, A. G. de Oliveira1, and D. Ugarte2 North Carolina State University, Analytical Instrumentation Facility, Raleigh-NC, 27695-7531, U.S.A. 1 Universidade Federal de Minas Gerais, Depto. de Física, Belo Horizonte-MG, Brazil 2 Laboratório Nacional de Luz Síncrotron, Campinas-SP, Brazil
ABSTRACT
In this work, we report optical and structural properties of vertical aligned self-assembled InAs quantum dots multilayers. The InAs quantum dots samples were grown by Molecular Beam Epitaxy. Employing Atomic Force Microscopy, Transmission Electron Microscopy, and Gracing Incident X-ray Diffraction we have studied the structural properties of samples with different number of periods of the multiplayer structure, as well as different InAs coverage. The optical properties were studied using Photoluminescence spectroscopy.
INTRODUCTION
Recently, self-assembled InAs quantum dots (QDs) in GaAs have received considerable attention for fundamental studies on semiconductor devices. When growing InAs epitaxially on GaAs (100) substrates, the lattice misfit (7%) between InAs and the GaAs causes coherency stresses and strains. In order to reduce the corresponding distortion energy, the epilayer grows in the Stranski–Krastanov mode1. After a wetting layer (WL) of approximately 1.6 monolayers (ML), the excess of InAs relaxes elastically by forming three-dimensional (3D) islands. Capping the InAs with a GaAs spacer layer, and by iterating the deposition of InAs layers and GaAs spacers, multilayers of InAs QDs are produced. Moreover, the coherency of the stresses between InAs and GaAs leads, for relative thin GaAs spacer, to a vertical alignment of the QDs: when overgrowing the InAs layer with an epitaxial layer of GaAs, the lattice misfit between the two materials causes a lateral expansion in the GaAs surface above the buried InAs QDs. This locally reduces the misfit to the following InAs layer and induces the new islands to be formed right above the buried islands of the previous InAs layer2. The above procedure has great potential for realizing high-density regular array of quantum dots3. However, in order to obtain buried islands with a narrow size distribution and vertical alignment optimization of different growth parameters is needed. In this work, we present experimental results on InAs QDs multilayers. We studied the influence of the number of periods on the morphological and optical properties of the samples by using Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), Photoluminescence spectroscopy (PL), and Gracing Incidence X-ray Diffraction (GID). Y8.24.1
Table I. Characteristics of the samples. Were n is the number of periods, θInAs is the InAs coverage, DGaAs is the thickness of the GaAs spacer layer, ρ is the density of islands, lm is the mean distance between islands, and Vm is the mean volume of th
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