Deep levels in GaAs(001)/InAs/InGaAs/GaAs self-assembled quantum dot structures and their effect on quantum dot devices (original) (raw)
Related papers
Critical barrier thickness for the formation of InGaAs/GaAs quantum dots
Materials Science and Engineering: C, 2005
The discovery of self-assembled quantum dots (QDs) has attracte because of its possible applications in optoelectronic devices. The low density of QDs formed makes it useful to grow several layers of dots in the form of a stacked structure. In these structures, the buried islands tend to influence the further nucleation of islands in subsequent layers. It has been experimentally found that, when the number of layers increases, island sizes and shapes become more regular with each successive layer.
Journal of Alloys and Compounds, 2017
This study investigates the vertical inter-QDs spacing (VIDS) in a coupled bilayer quantum dots (CBQD) heterostructure using cross-sectional High Resolution Transmission Electron Microscopy (HRTEM). Simultaneously, we also examined the interrelationship of VIDS with the strain energy inside the CBQD stack. As a continuation, the CBQD heterostructure were further explored from different aspects of growth parameters, such as the deposition of ultrathin GaAs spacer layer of 4.0-4.5 nm between the seed and active layer of QDs, the effect of larger monolayer coverage (3.2 ML) of seed layer QDs, and the optimization of growth rates for the CBQDs. Moreover, we present a model technique to characterize the in-plane 2ߠ߯/ߔ of InAs QDs and GaAs at (002) and (004) planes in order to analyze the strain. This study was the first of its kind to look at the formation of self-assembled In (x) Ga (1-x) As layer at the interface across the ultrathin GaAs spacer and InAs QDs, verified with HRTEM images. Smaller size of QDs formed in the seed layer led to the formation of a non-uniform self-assembled In (x) Ga (1-x) As layer. The problem of non-uniformity of In (x) Ga (1-x) As layer was resolved by increasing the seed layer
We report a theoretical study of the wetting layer thickness, In x Ga (1Àx) As quantum-well thickness and Indium composition effects on the physical properties of InAs quantum dots (QDs) and quantum dots-in-well (QD-in-WELL) grown on GaAs high index substrates. Finite element method is used to calculate the strain, piezoelectric field distributions and the electronic structure. Coulomb interaction has been taken as a perturbation in the interband transition energy. The groundestate transition energy is influenced by the wetting layer thickness (WL) and the substrate orientation; however, it is not affected by the InGaAs quantum-well thickness. We have found that the tensile strain at the interface is the main factor responsible for the difficulty of self-assembled InAs QDs formation on GaAs(111) substrate. On the other hand, the stability of the relaxed strain into QDeINeWELL depended on the Indium composition and the quantum-well thickness as well as the orientation substrate. The appropriate Indium composition in the InGaAs quantum-well is found to be 0.3 for the QDeINeWELL grown on GaAs(111) and 0.2 for the QDeIN eWELL grown on GaAs(119). This work can be helpful to controlling the wavelength of QDeINeWELL grown on high index substrates by changing the In composition or the quantum well-thickness.
Quantum Dots and Nanostructures: Synthesis, Characterization, and Modeling Xi, 2014
The development of epitaxial technology for the fabrication of quantum dot (QD) gain material operating in the 1.55 µm wavelength range is a key requirement for the evolvement of telecommunication. High performance QD material demonstrated on GaAs only covers the wavelength region 1-1.35 µm. In order to extract the QD benefits for the longer telecommunication wavelength range the technology of QD fabrication should be developed for InP based materials. In our work, we take advantage of both QD fabrication methods Stranski-Krastanow (SK) and selective area growth (SAG) employing block copolymer lithography. Due to the lower lattice mismatch of InAs/InP compared to InAs/GaAs, InP based QDs have a larger diameter and are shallower compared to GaAs based dots. This shape causes low carrier localization and small energy level separation which leads to a high threshold current, high temperature dependence, and low laser quantum efficiency. Here, we demonstrate that with tailored growth conditions, which suppress surface migration of adatoms during the SK QD formation, much smaller base diameter (13.6nm versus 23nm) and an improved aspect ratio are achieved. In order to gain advantage of non-strain dependent QD formation, we have developed SAG, for which the growth occurs only in the nano-openings of a mask covering the wafer surface. In this case, a wide range of QD composition can be chosen. This method yields high purity material and provides significant freedom for reducing the aspect ratio of QDs with the possibility to approach an ideal QD shape. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/12/2014 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 8996 899606-2 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/12/2014 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 8996 899606-7 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/12/2014 Terms of Use: http://spiedl.org/terms
Applied Physics Letters, 2010
The effect of postgrowth annealing on shape and ordering of a single layer of InGaAs/GaAs͑001͒ quantum dots is investigated by three dimensional grazing incidence small angle x-ray scattering. A transition from disordered dots to two-dimensional lateral ordering is found. This transition is accompanying a quantum dot shape transformation. Grazing incidence diffraction measurements relate the observed ordering type to strain driven self organization. The role of different growth conditions leading to lateral correlation is discussed by comparing the results to recent experimental achievements in the field.
Wafer-scale epitaxial modulation of quantum dot density
Nature Communications
Precise control of the properties of semiconductor quantum dots (QDs) is vital for creating novel devices for quantum photonics and advanced opto-electronics. Suitable low QD-densities for single QD devices and experiments are challenging to control during epitaxy and are typically found only in limited regions of the wafer. Here, we demonstrate how conventional molecular beam epitaxy (MBE) can be used to modulate the density of optically active QDs in one- and two- dimensional patterns, while still retaining excellent quality. We find that material thickness gradients during layer-by-layer growth result in surface roughness modulations across the whole wafer. Growth on such templates strongly influences the QD nucleation probability. We obtain density modulations between 1 and 10 QDs/µm2 and periods ranging from several millimeters down to at least a few hundred microns. This method is universal and expected to be applicable to a wide variety of different semiconductor material sys...
Effects of the quantum dot ripening in high-coverage InAs/GaAs nanostructures
Journal of Applied Physics, 2007
We report a detailed study of InAs/ GaAs quantum dot ͑QD͒ structures grown by molecular beam epitaxy with InAs coverages continuously graded from 1.5 to 2.9 ML. The effect of coverage on the properties of QD structures was investigated by combining atomic force microscopy, transmission electron microscopy, x-ray diffraction, photoluminescence, capacitance-voltage, and deep level transient spectroscopy. In the 1.5-2.9 ML range small-sized coherent QDs are formed with diameters and densities that increase up to 15 nm and 2 ϫ 10 11 cm −2 , respectively. For Ͼ 2.4 ML large-sized QDs with diameters of 25 nm and densities ranging from 2 ϫ 10 8 to 1.5 ϫ 10 9 cm −2 coexist with small-sized QDs. We explain the occurrence of large-sized QDs as the inevitable consequence of ripening, as predicted for highly lattice-mismatched systems under thermodynamic equilibrium conditions, when the coverage of the epitaxial layer exceeds a critical value. The fraction of ripened islands which plastically relax increases with , leading to the formation of V-shaped defects at the interface between QDs and upper confining layers that propagate toward the surface. Island relaxation substantially affects the properties of QD structures: ͑i͒ free carrier concentration is reduced near the QD plane, ͑ii͒ the QD photoluminescence intensity is significantly quenched, and ͑iii͒ deep levels show up with typical features related to extended structural defects.