Understanding polarization properties of InAs quantum dots by atomistic modeling of growth dynamics (original) (raw)
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Tailoring electronic and optical properties of self-assembled InAs quantum dots (QDs) is a critical limit for the design of several QD-based optoelectronic devices operating in the telecom frequency range. We describe how a fine control of the strain-induced surface kinetics during the growth of vertically-stacked multiple layers of QDs allow to engineer their self organization process. Most noticeably, the present study shows that the underlying strain field induced along a QD stack can be modulated and controlled by time-dependent intermixing and segregation effects occurring after capping with GaAs spacer. This leads to a drastic increase of TM/TE polarization ratio of emitted light, not accessible from the conventional growth parameters. Our detailed experimental measurements supported by comprehensive multi-million atom simulations of strain, electronic, and optical properties, provide in-depth analysis of the grown QD samples leading us to depict a clear picture on atomic scale phenomena affecting the proposed growth dynamics and consequent QD polarization response.
Shape transition during epitaxial growth of InAs quantum dots on GaAs(001): Theory and experiment
Physical Review B, 2006
For heteroepitaxial growth of InAs islands on GaAs͑001͒, a transition of shapes is observed experimentally by scanning-tunneling microscopy and analyzed theoretically in terms of the thermodynamic stability of the islands. The experiments show the coexistence of small islands bound predominantly by shallow facets of the ͕137͖ family and large islands that show a variety of steeper facets, among them the ͕101͖, ͕111͖, and ͕111͖ orientations. The calculations of island stability employ a hybrid approach, where the elastic strain relief in the islands is calculated by continuum elasticity theory, while surface energies and surface stresses are taken from density-functional theory calculations that take into account the atomic structure of the various side facets, as well as of the InAs wetting layer on GaAs͑001͒. With the help of the theoretical analysis, we interpret the observed coexistence of shapes in terms of a structural phase transition accompanied by a discontinuous change of the chemical potential in the islands. Consequences of this finding are discussed in analogy with a similar behavior of GeSi islands on silicon observed previously.
Materials, 2015
This work reports on theoretical and experimental investigation of the impact of InAs quantum dots (QDs) position with respect to InGaAs strain reducing layer (SRL). The investigated samples are grown by molecular beam epitaxy and characterized by photoluminescence spectroscopy (PL). The QDs optical transition energies have been calculated by solving the three dimensional Schrödinger equation using the finite element methods and taking into account the strain induced by the lattice mismatch. We have considered a lens shaped InAs QDs in a pure GaAs matrix and either with InGaAs strain reducing cap layer or underlying layer. The correlation between numerical calculation and PL measurements allowed us to track the mean buried QDs size evolution with respect to the surrounding matrix composition. The simulations reveal that the buried QDs' realistic size is less than that experimentally driven from atomic force microscopy observation. Furthermore, the average size is found to be slightly increased for InGaAs capped QDs and dramatically decreased for QDs with InGaAs under layer.
Intermixing and shape changes during the formation of InAs self-assembled quantum dots
Applied Physics Letters, 1997
The initial stages of GaAs overgrowth over self-assembled coherently strained InAs quantum dots (QDs) are studied. For small GaAs coverages (below 5 nm), atomic force microscopy (AFM) images show partially covered island structures with a regular size distribution which are elongated in the [011] direction. Analysis of the AFM profiles show that a large anisotropic redistribution of the island material
Physica B: Condensed Matter, 2014
We report on a simple theoretical model allowing to investigate the rapid thermal annealing induced quantum dots intermixing and consequent inhomogeneous broadening. In this model, where the 3D Schrodinger equation has been solved, by the orthonormal wave function expansion method, for strained InAs QD, we assume a lens-shaped QD with a uniform indium composition and a constant aspect ratio during the intermixing process. The size and aspect ratio for as-grown InAs QD, have been estimated by matching the calculated interband optical transition energies to the experimental photoluminescence emission peaks from ground and excited states. The simulated results were correlated with photoluminescence data at various annealing temperatures. Keeping constant the QD aspect ratio, a good agreement has been found between experimental and calculated emission energies for different indium atomic diffusion lengths. Small QDs are found to be more sensitive to the intermixing than larger QDs. This study allows also to calculate the full width at half maximum (FWHM) and compare it with the experimental value. The theoretical calculations suggest that the origin of the inhomogeneous broadening is mainly related to the variation of the QDs size.
Modification of InAs quantum dot structure by the growth of the capping layer
Applied Physics Letters, 1998
InAs quantum dots inserted at the middle of a GaAs quantum well structure have been investigated by transmission electron microscopy and scanning transmission electron microscopy. We find that the growth condition of the overlayer on the InAs dots can lead to drastic changes in the structure of the dots. We attribute the changes to a combination of factors such as preferential growth of the overlayer above the wetting layers because of the strained surfaces and to the thermal instability of the InAs dots at elevated temperature. The result suggests that controlled sublimation, through suitable manipulation of the overlayer growth conditions, can be an effective tool to improve the structure of the self-organized quantum dots and can help tailor their physical properties to any specific requirements of the device applications.
Strain engineering of self-organized InAs quantum dots
Physical Review B, 2001
The effects of a thin gallium-rich In x Ga 1Ϫx As cap layer on the electronic properties of self-organized InAs quantum dots ͑QD's͒ are investigated both experimentally and theoretically. Increasing the indium concentration of the cap layer allows tuning the ground state transition to lower energies maintaining strong quantization of the electronic states. Strain-driven partial decomposition of the In x Ga 1Ϫx As cap layer increases the effective QD size during growth and the altered barrier composition leads to a partial strain relaxation within the capped InAs QD's. Strain engineering the structural properties of the QD's as well as the actual confining potential offers a pathway to control the electronic properties, e.g., to shift the emission wavelength of lasers based on self-organized InAs QD's to the infrared.
Journal of Crystal Growth, 2002
We investigated the maximum density of InAs quantum dots grown by molecular beam epitaxy on GaAs(0 0 1) substrates. Different from most current work, we took advantage of the non-uniformity of the molecular beams to produce a sample in which the amount of InAs material was continuously varied across the surface in order to analyze the evolution of the QDs as a function of the film thickness. A density of structures as high as 1800 mm À2 could be observed by atomic force microscopy and is around twice the maximum value typically reported in the literature. No loss of size uniformity was detected for such a high density.
Correlating structure, strain, and morphology of self-assembled InAs quantum dots on GaAs
Applied Physics Letters, 2011
We report on the use of a direct x-ray phase retrieval method, coherent Bragg rod analysis, to characterize self-assembled InAs quantum dots (QDs) grown epitaxially on GaAs substrates. Electron density maps obtained close to the x-ray absorption edges of the constituent elements are compared to deconvolute composition and atomic spacing information. Our measurements show no evidence of a wetting layer and reveal bowing of the atomic layers throughout the QD, extending from the QD-substrate interface. This leads to a half-layer stacking shift which may act to partially decouple the QDs electronically from the substrate.
Nanotechnology, 2012
III-V growth and surface conditions strongly influence the physical structure and resulting optical properties of self-assembled quantum dots (QDs). Beyond the design of a desired active optical wavelength, the polarization response of QDs is of particular interest for optical communications and quantum information science. Previous theoretical studies based on a pure InAs QD model failed to reproduce experimentally observed polarization properties. In this work, multi-million atom simulations are performed to understand the correlation between chemical composition and polarization properties of QDs. A systematic analysis of QD structural parameters leads us to propose a two layer composition model, mimicking In segregation and In-Ga intermixing effects. This model, consistent with mostly accepted compositional findings, allows to accurately fit the experimental PL spectra. The detailed study of QD morphology parameters presented here serves as a tool for using growth dynamics to engineer the strain field inside and around the QD structures, allowing tuning of the polarization response.