InAs/GaAs quantum dot structures covered by InGaAs strain reducing layer characterized by photomodulated reflectance (original) (raw)
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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
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.
Quantum dot strain engineering of InAs/ InGaAs nanostructures
We present a complete study both by experiments and by model calculations of quantum dot strain engineering, by which a few optical properties of quantum dot nanostructures can be tailored using the strain of quantum dots as a parameter. This approach can be used to redshift beyond 1.31 m and, possibly, towards 1.55 m the room-temperature light emission of InAs quantum dots embedded in InGaAs confining layers grown on GaAs substrates. We show that by controlling simultaneously the lower confining layer thickness and the confining layers' composition, the energy gap of the quantum dot material and the band discontinuities in the quantum dot nanostructure can be predetermined and then the light emission can be tuned in the spectral region of interest. The availability of two degrees of freedom allows for the control of two parameters, which are the emission energy and the emission efficiency at room temperature. The InAs/ InGaAs structures were grown by the combined use of molecular beam epitaxy and atomic layer molecular beam epitaxy; their properties were studied by photoluminescence and photoreflectance spectroscopies and by atomic force microscopy; in particular, by means of photoreflectance not only the spectral features related to quantum dots were studied but also those of confining and wetting layers. The proposed approach has been used to redshift the room-temperature light emission wavelength up to 1.44 m. The optical results were analyzed by a simple effective-mass model that also offers a rationale for engineering the properties of structures for efficient long-wavelength operation.
Superlattices and Microstructures, 2014
Photoluminescence (PL) of InAs quantum dots (QDs) embedded in the Al 0.30 Ga 0.70 As/In 0.15 Ga 0.85 As/InGaAlAs/GaAs quantum wells (QWs) have been investigated in the temperature range of 10-500 K for as grown samples and after thermal annealing at 640°C or 710°C for two hours. QD samples with the different InAlGaAs capping layers (GaAs or Al 0.1 Ga 0.75 In 0.15 As) have been studied. The higher PL intensity and lower energy of ground state (GS) emission are detected in the structure with Al 0.1 Ga 0.75 In 0.15 As layer. This QD structure in as grown state has smaller PL thermal decay in comparison with this parameter in the structure with GaAs layer. The variation of PL intensities and peak positions at annealing are more essential in the QD structure with Al 0.1 Ga 0.75 In 0.15 As capping layer, apparently, due to more efficient Ga(Al)/In intermixing.
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.
Journal of Materials Science: Materials in Electronics, 2017
characterized by non-homogeneities of QD sizes, QD compositions, QD densities and emission intensities resulting in difficulties in predicting the optical and electrical device parameters [1-8]. It was shown that the InAs QD density has been enlarged if the InAs QDs were grown on the surface of the In x Ga 1−x As buffer layer within of In x Ga 1−x As/ GaAs QWs [14]. In these structures the PL intensity was enhanced owing to the better crystal quality of surrounding QD materials [15, 16], as well as more effective the exciton capture into QWs and QDs [17-21]. Recently it was revealed that the PL intensity and PL peak positions of InAs QD emissions versus InGaAs capping layer compositions vary no monotonically [14, 16]. One of the reasons of such effect can be related to the different levels of elastic strains in In x Ga 1−x As/GaAs QWs, which depend on In x Ga 1−x As compositions. To study the strain related effects in QD structures, HR-XRD scans for the symmetrical Bragg reflection have been used. XRD and HR-XRD studies, as well as fitting the obtained HR-XRD results, permit to estimate the thickness and composition of QW layers, the level of elastic strain and its impact on InAs QD parameters in the In x Ga 1−x As/GaAs QW structures with the different In compositions in capping In x Ga 1−x As layers. 2 Experimental conditions InAs QD structures were created using the molecular beam epitaxial (MBE) growth on the (001) oriented 2′'diameter semi-insulating GaAs substrates. Each structure included a 300 nm GaAs buffer layer and a 70 nm GaAs upper final capping layer grown at 600 °C (Fig. 1). Between GaAs layers three self-organized InAs QD arrays (formed by depositing 2.4 ML of InAs at 490 °C) Abstract GaAs/In 0.15 Ga 0.85 As/In x Ga 1−x As/GaAs quantum wells (QWs) with embedded InAs quantum dots (QDs) and with variable In compositions in capping In x Ga 1−x As layers (0.10 ≤ x ≤ 0.25) have been studied by means of photoluminescence, X ray diffraction (XRD) and high resolution XRD (HR-XRD) methods. In x Ga 1−x As composition varying is accompanied by changing no monotonically the PL spectrum parameters of InAs QDs and by decreasing the InAs QD sizes. XRD and HR-XRD studies permit to control the InGaAs layer compositions and elastic strains in QWs. The analysis of HR-XRD results has shown that the level of elastic strain varies no monotonically in studied QD structures as well. The physical reasons of mentioned optical and structural effects and their dependences on capping layer compositions have been discussed.
The effect of strain on tuning of light emission energy of InAs/InGaAs quantum-dot nanostructures
Applied Physics Letters, 2003
We prepared by molecular-beam epitaxy and studied structures of InAs quantum dots embedded in InxGa1-xAs confining layers. The structures were designed so that the strain of quantum dots could be controlled independently of In composition of confining layers. In such a way, we single out the effect of strain in quantum dots on the energy of photoluminescence emission. We show that strain can be effectively used to tune the emission energy of quantum dots, and that room-temperature emission at 1.3 μm can be obtained. Our results suggest that by quantum-dot strain engineering, it will be possible to extend emission wavelength beyond 1.55 μm.
Improvement of InAs quantum-dot optical properties by strain compensation with GaNAs capping layers
Applied Physics Letters, 2003
Two kinds of self-assembled InAs quantum dots ͑QDs͒ grown on GaAs ͑001͒ substrates were studied. One is capped with GaAs layers and the other with GaNAs strain-compensating layers. Photoluminescence ͑PL͒ measurements on the two kinds of InAs QDs showed distinct dependence on the selection of the capping layers. The homogeneity and luminescence efficiency of the InAs QDs were much improved when the net strain was reduced with GaNAs layers. These results demonstrate the importance of net strain compensation for the improved optical quality of InAs QDs.
Journal of Applied Physics, 2002
Self-assembled InAs quantum dots ͑QDs͒ embedded in GaN 0.007 As 0.993 strain compensating layers have been grown by metalorganic-molecular-beam epitaxy on a GaAs ͑001͒ substrate with a high density of 1ϫ10 11 cm Ϫ2 . The photoluminescence properties have been studied for two periods of InAs quantum dots layers embedded in GaN 0.007 As 0.993 strain compensating layers. Four well-resolved excited-state peaks in the photoluminescence spectra have been observed from these highly packed InAs QDs embedded in the GaN 0.007 As 0.993 strain compensating layers. This indicates that the InAs QDs are uniformly formed and that the excited states in QDs due to the quantum confinement effect are well defined. This is explained by tensile strain in GaNAs layers instead of the usual GaAs layers to relieve the compressive strain formed in InAs QDs to keep the total strain of the system at a minimum.
Superlattices and Microstructures, 2018
GaAs/Al 0.30 Ga 0.70 As quantum wells (QWs) with InAs quantum dot (QD) arrays covered by the different capping layers: Al 0.30 Ga 0.70 As or Al 0.1 Ga 0.75 In 0.15 As, have been investigated by means of the photoluminescence (PL) and high resolution X-ray diffraction (HR-XRD) methods. It is revealed that the QD emission in the structure with Al 0.1 Ga 0.75 In 0.15 As capping is characterized by the lower PL energy, higher PL intensity of ground state emission and smaller its full width at half maximum (FWHM) in comparison with ground state QD emission at Al 0.30 Ga 0.70 As capping. The analysis of PL and HR-XRD scans has shown that the strain relaxation at high QW growth temperatures in the structure with Al 0.30 Ga 0.70 As capping was connected with changing significantly the material compositions of the QDs and capping layer. As a result the QD emission shifts into the higher energy range, the PL intensity decreases and the FWHMs of PL bands increase. In contrary, in the structure with Al 0.1 Ga 0.75 In 0.15 As capping the strain relaxation manifests itself by decreasing the InAs QD heights without changing the InAs QD material composition. The advantage of Al 0.1 Ga 0.75 In 0.15 As capping has been discussed.