Effect of post-growth annealing on the optical properties of InAs / GaAs quantum dots: A tight-binding study. J. Appl. Phys. (2007), 102(2), 23711. (original) (raw)
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Structural and optical properties of InAs–GaAs quantum dots subjected to high temperature annealing
Applied Physics Letters, 1996
Annealing at higher temperature ͑700°C͒ of structures with two-dimensional and three-dimensional arrays in InAs-GaAs quantum dots ͑QDs͒ results in an increase in the size and in a corresponding decrease in the indium composition of the QDs. The change in the In composition is monitored by the contrast pattern in the plan-view transmission electron microscopy ͑TEM͒ images viewed under the strong beam imaging conditions. Increase in the size of the QDs is manifested by the plan-view TEM images taken under ͓001͔ zone axis illumination as well as by the cross-section TEM images. We show that the dots maintain their geometrical shape upon annealing. Luminescence spectra demonstrate a shift of the QD luminescence peak toward higher energies with an increase in the annealing time ͑10-60 min͒ in agreement with the decrease in indium composition revealed in TEM studies. The corresponding decrease in the QD localization energy results in an effective evaporation of carriers from QDs at room temperature, and the intensity of the QD luminescence decreases, and the intensity of the wetting layer and the GaAs matrix luminescence increase with the increase in the annealing time.
Effect of the In (Ga) inter-diffusion on the optical properties in InAs/GaAs annealed quantum dots
Journal of Physics: Conference Series, 2010
We theoretically consider the effect of post growth annealing on the electron-hole interaction in the self-assembled InAs/GaAs Quantum Dots (QD). We offer a numerical model of the QD which is based on an experiments data with such heterostructure. Our model allows us to simulate the process of annealing and to calculate the distribution profiles of (In and Ga) atoms over the heterostructure. Using this model we have calculated the energy states of carriers and the optical transition in annealed QDs. We used the parameters of our model referring to the experimental data on Photoluminescence (PL) spectra for a set of heterostructure with InAs/GaAs annealed at different temperatures and we are shown the effects of the interdiffusion into QD on the optical properties which explain the tuning of PL profiles caused by the diffusion of In atoms from QDs into the barrier layers and leads to this modification in these profiles.
InAs/GaAs pyramidal quantum dots: Strain distribution, optical phonons, and electronic structure
Physical Review B, 1995
The strain distribution in and around pyramidal InAs/GaAs quantum dots (QD's) on a thin wetting layer fabricated recently with molecular-beam epitaxy, is simulated numerically. For comparison analytical solutions for the strain distribution in and around a pseudomorphic slab, cylinder, and sphere are given for isotropic materials, representing a guideline for the understanding of strain distribution in two-, one-, and zero-dimensional pseudomorphic nanostructures. For the pyramidal dots we find that the hydrostatic strain is mostly confined in the QD; in contrast part of the anisotropic strain is from the QD into the barrier. The optical-phonon energies in the QD are estimated and agree perfectly with recent experimental findings. From the variation of the strain tensor the local band-gap modification is calculated. Piezoelectric effects are additionally taken into account. The threedimensional effective-mass single-particle Schrodinger equation is solved for electrons and holes using the realistic confinement potentials. Since the QD s are in the strong confinement regime, the Coulomb interaction can be treated as a perturbation. The thus obtained electronic structure agrees with luminescence data. Additionally A1As barriers are considered.
Growth and properties of InAs/InxGa1−xAs/GaAs quantum dot structures
Journal of Crystal Growth, 2008
Single-and double-layer InAs/GaAs quantum dot structures with strain-reducing layers (SRLs) were prepared by metalorganic vaporphase epitaxy using the Stranski-Krastanow growth mode. Structures were studied in-situ by reflectance anisotropy spectroscopy (RAS), and ex-situ by photoluminescence (PL). These structures, with very intense room temperature PL at wavelengths from 1.25 to 1.55 mm according to growth and structure parameters, were grown along while monitored with RAS. Strong correlation between RAS signal and PL intensity was found. Dependence of PL emission maximum position on SRL composition and capping layer thickness is shown. r
We present an atomistic investigation of the influence of strain on the electronic properties of quantum dots QD's within the empirical sp 3 s* tight-binding ETB model with interactions up to second nearest neighbors and spin-orbit coupling. Results for the model system of capped pyramid-shaped InAs QD's in GaAs, with supercells containing 10 5 atoms are presented and compared with previous empirical pseudopotential results. The good agreement shows that ETB is a reliable alternative for an atomistic treatment. The strain is incorporated through the atomistic valence-force field model. The ETB treatment allows for the effects of bond length and bond angle deviations from the ideal InAs and GaAs zinc-blende structure to be selectively removed from the electronic-structure calculation, giving quantitative information on the importance of strain effects on the bound-state energies and on the physical origin of the spatial elongation of the wave functions. Effects of dot-dot coupling have also been examined to determine the relative weight of both strain field and wave-function overlap.
Materials Research-ibero-american Journal of Materials, 2004
A systematic investigation of the properties of the InAs/GaAs self-assembled quantum dots (SAQDs) system subjected to a post-growth annealing using capacitance-voltage, Raman scattering and photoluminescence measurements is presented. The application of both electrical and optical methods allowed us to obtain reliable information on the microscopic structural evolution of this system. The single layer and the multilayer quantum dots were found to respond differently to the annealing process, due to the differences in strain that occur in both systems. The diffusion activated by strain provoked the appearance of an InGaAs alloy layer in substitution to the quantum dots layers; this change occurred at the annealing temperature T = 600 °C in the multilayer system. A single dot layer, however, was observed even after the annealing at T = 700 °C. Moreover, the low temperature annealing was found to improve the homogeneity of the multilayer system and to decrease the electrical interlayer coupling.
Physical Review B, 2003
We present an atomistic investigation of the influence of strain on the electronic properties of quantum dots (QD's) within the empirical sp 3 s * tight-binding (ETB) model with interactions up to 2nd nearest neighbors and spin-orbit coupling. Results for the model system of capped pyramid-shaped InAs QD's in GaAs, with supercells containing ∼ 10 5 atoms are presented and compared with previous empirical pseudopotential results. The good agreement shows that ETB is a reliable alternative for an atomistic treatment. The strain is incorporated through the atomistic valence force field model. The ETB treatment allows for the effects of bond length and bond angle deviations from the ideal InAs and GaAs zincblende structure to be selectively removed from the electronic-structure calculation, giving quantitative information on the importance of strain effects on the bound state energies and on the physical origin of the spatial elongation of the wave functions. Effects of dot-dot coupling have also been examined to determine the relative weight of both strain field and wave function overlap.
Strain and optical transitions in InAs quantum dots on (001) GaAs
Superlattices and Microstructures, 2001
To investigate the strain characteristics of InAs quantum dots grown on (001) GaAs by solid source molecular beam epitaxy we have compared calculated transition energies with those obtained from photoluminescence measurements. Atomic force microscopy shows the typical lateral size of the quantum dots as 20-22 nm with a height of 10-12 nm, and photoluminescence spectra show strong emission at 1.26 µm when the sample is capped with a GaAs layer. The luminescence peak wavelength is red-shifted to 1.33 µm when the dots are capped by an In 0.4 Ga 0.6 As layer. Excluding the strain it is shown that the theoretical expectation of the ground-state optical transition energy is only 0.566 eV (2.19 µm), whereas a model with three-dimensionally-distributed strain results in a transition energy of 0.989 eV (1.25 µm). It has thus been concluded that the InAs quantum dot is spatially strained. The InGaAs capping layer reduces the effective barrier height so that the transition energy becomes red-shifted.