Effect of annealing on the structure and optical properties of InGaAs/GaAs quantum dots (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.
Technical Physics Letters, 2002
The optical and structural properties of heterostructures with quantum dots (QDs) in the InAs/GaAs system overgrown with an InGaAs solid solution were studied. The QD layers were obtained using different molecular beam deposition techniques: molecular beam epitaxy versus submonolayer migration-stimulated epitaxy. The photoluminescence peaks in the spectra of samples with overgrown QD layers occur in the wavelength range from 1.18 to 1.32 µ m. It was found that the growth conditions also influence the electronic structure of QDs.
Influence of In/Ga intermixing on the optical properties of InGaAs/GaAs quantum dots
Journal of Crystal Growth, 1998
We report on the impact of thermal annealing of buried InGaAs quantum dots (QDs) on the eigenstate energies and their inhomogeneous broadening due to size fluctuations. Application of annealing temperatures (¹) of up to 700°C for 30 min results in a blue shift of the QD ground state luminescence of 150 meV accompanied by a strong reduction of sublevel separation and inhomogeneous broadening. At the same time the wetting layer luminescence is only slightly shifted, resulting in a strongly decreased localization energy of the QDs. With increasing annealing temperature the photoluminescence peak broadening due to the QDs size distribution shows a distinct maximum and subsequently decreases below the value of as grown QDs. These observations qualitatively agree with calculations for a simple model system of spherical QDs assuming Fickian interdiffusion of dot and barrier material. Our results demonstrate that the growth temperatures (¹ %) applied after deposition of the QDs strongly affect their properties. Thus for fabrication of QD based devices in the InGaAs/GaAs system a compromise for the choice of ¹ % has to be made in order to achieve both high carrier localization energies in the QDs (low ¹ %) and high material quality of the cap layers (high ¹ %).
Japanese Journal of Applied Physics, 2000
We have studied the effects of annealing a self-organized InGaAs/GaAs quantum dot sample between 580 and 700°C by magnetoluminescence measurements at 2 K and fields up to 15 T. High-excitation power density luminescence spectra reveal up to three features in addition to the ground-state emission arising from radiative recombination processes between excited states of the quantum dots. With increasing annealing temperature all emission lines shift to higher energies while varying their splittings indicating a systematic increase in volume and Ga content of the dots. From the diamagnetic shift and the Zeeman splitting of the ground-state emission we obtain an increase of the spatial extent of the exciton wave function but a decrease of the effective g-factor upon annealing. The magnetic field splittings of excited-state transitions exhibit a strong dependence on annealing and are well accounted for within a simple oscillator model with total angular momentum mainly determined by the d...
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.
We present an atomistic study of the strain field, the one-particle electronic spectrum and the oscillator strength of the fundamental optical transition in chemically disordered InxGa1−xAs pyramidal quantum dots QDs. Interdiffusion across the interfaces of an originally “pure” InAs dot buried in a GaAs matrix is simulated through a simple model, leading to atomic configurations where the abrupt heterointerfaces are replaced by a spatially inhomogeneous composition profile x. Structural relaxation and the strain field calculations are performed through the Keating valence force field model, while the electronic and optical properties are determined within the empirical tight-binding approach. We analyze the relative impact of two different aspects of the chemical disorder, namely: i the effect of the strain relief inside the QD, and ii the purely chemical effect due to the group-III atomic species interdiffusion. We find that these effects may be quantitatively comparable, significantly affecting the electronic and optical properties of the dot. Our results are discussed in comparison with recent luminescence studies of intermixed QDs.
Excitation Density and Temperature Dependent Photoluminescence of InGaAs Self-Assembled Quantum Dots
Japanese Journal of Applied Physics, 1999
In this paper, we shall report on the excitation density and temperature dependent photoluminescence produced by discrete energy levels from InGaAs self-assembled quantum dots. While increasing the photoexcitation density, five peaks originating from discrete energy levels of quantum dot and wetting layer are observed. By deconvoluting these spectra using multiple Gaussian fit, the intensity of each state is saturated following its degeneracy. We describe the lateral confinement of quantum dots using a parabolic potential model. The saturated values are in good agreement with the degeneracy of this potential type. From the temperature dependent photoluminescence, we observed the thermally activated quenching of each state. Our results suggest that the wetting layer acts as a barrier to the carrier thermallization processes offering a two dimensional path for inter-dot coupling.
The INGAAS/GAAS Quantum Dots Under Effective and Ab Initio Treatments: Comparison and Results
2009
The 3D model for InGaAs/GaAs quantum dots (QD), based on a single sub-band approach taking into account the effect of non-parabolicity of the conduction band is presented. We apply an effective approach in which the combined effect of strain, piezoelectricity and interband interactions are simulated by an effective potential. The strength of the effective potential is determined by analysis of capacitance-gate-voltage (CV) data and photoluminescence spectra for QDs and quantum rings (QR). The model is compared with one based on the 8band kp-theory, which takes into account interband interactions, strain and piezoelectric effects in an ab initio manner. The atomistic pseudopotential approach is also taken for comparison. It is found that disagreements between predictions obtained in the framework of our model and of these models are related to strength of the electron confinement. It is shown that our approach accurately reproduces photoluminescence measurements for excitons when the...
Photoluminescence studies of InAs/GaAs quantum dots covered by InGaAs layers
Materials Science and Engineering: B, 2010
Photoluminescence (PL), PL excitation (PLE), and time-resolved PL were used to study effects of InGaAs layers on the optical properties of InAs/GaAs quantum dots (QDs). A rich fine structure in the excited states of confined excitons (up to n = 4 quantum states) was observed, providing useful information to study the quantum states in the InAs/GaAs QDs. A significant redshift of the PL peak energy for the QDs covered by InGaAs layers was observed, attributing to the decrease of the QD strain and the lowing of the quantum confinement.