Influence of GaAsSb structural properties on the optical properties of InAs/GaAsSb quantum dots

The optical properties of InAs quantum dots with GaAsSb buffer, capping and cladding layers of different alloy compositions are studied by photoluminescence techniques. Fully strained GaAsSb layers show that the inclusion of a buffer layer gives a blue-shift to quantum dot emission, while for quantum dots capped with GaAsSb a clear red-shift is seen. Power-dependent photoluminescence suggests a transition from type-I to type-II can be achieved by GaAsSb at Sb composition between 11–13%, while the transition for the GaAsSb cladding layer occurs at around 11%. At low Sb composition, good crystal quality and energy barrier are detected by temperature-dependent photoluminescence, while high-level dislocation and defects exist under high antimony content, as evidenced by X-Ray Diffraction and Transmission Electron Microscopy.     

Electrodeposited quantum dots IV. Epitaxial short-range order in amorphous semiconductor nanostructures

The structure of diffraction-amorphous CdSe (a-CdSe) quantum dots (QDs) electrodeposited on evaporated Pd substrate was studied by high resolution transmission electron microscopy (HRTEM), and compared with epitaxial (crystalline) QDs obtained by the same procedure on Au, as well as with a simulated image of random a-CdSe. Digital analysis of HRTEM images established the existence of repeating ordered motifs in a-CdSe QDs on Pd substrates, in the form of epitaxial sub-nanometre to nanometre size clusters. The QDs are shown to be intermediate between crystalline and random amorphous material. Digital Fourier analysis indicated epitaxial relationship with the 111inPd substrate, rotated 30° relative to the orientational relationship on 111_Au.     

量子点液晶显示背光技术

量子点材料兼具极高的色纯度、发光颜色可调以及的荧光量子产率高等特点,已成为显示领域中的明星材料,在提升显示器件的色域方面具有巨大潜力。基于量子点材料的液晶显示背光技术是目前量子点材料在显示器件中的主流应用方向,引起了学术界和工业界的广泛关注。本文将综述量子点液晶显示背光技术的研究进展,主要包括量子点材料的选择、背光结构的应用以及材料复合与封装技术的发展现状,重点介绍了目前产业界广泛关注的量子点光学膜技术,特别是国内自主知识产权的低成本钙钛矿量子点光学膜技术,由于其具备广色域(124%NTSC)、易加工、低成本等特点,已成为具有成长潜力的技术路线。     

Colloidal quantum dots

The applications and physical properties of colloidal quantum dots are briefly reviewed and contrasted with those of Stransky–Krastanov grown quantum dots. To cite this article: P. Guyot-Sionnest, C. R. Physique 9 (2008).     

Oxidation behavior with quantum dots formation from amorphous GaAs thin films

ABSTRACT

We investigated the oxidation behaviour of an amorphous GaAs thin film deposited onto a micro/nanotextured Si surface by an electron beam. After the deposited film was exposed to air, microcrystallites were formed with octahedral cubic and monoclinic structures of arsenic oxides. Short time exposure after thin film deposition showed the formation of cubic arsenolite while long time exposure showed the formation of monoclinic claudetites as well as cubic arsenolites. These oxide microcrystallites at the GaAs thin film surface disappeared after the sample annealing process. However, the amorphous GaAs thin film included high-density GaAs nanodots. From UV and inverse photoemission spectroscopies, the thin film showed n-type band structure with an energy gap of 2.73?eV. Photoluminescence measurement showed an emission peak at (450–513)?nm with the energy of (2.41–2.75)?eV corresponding to dot size of (4.1–4.5)?nm.     

Correlations in quantum dots

The lowest excitations of a repulsively interacting few particle system are investigated within correlated “pocket state” basis functions. For long range interaction and non-isotropic confining potentials the method becomes exact, in the limit of large mean inter-particle distancesr _s. The multiplet structure of the many-electron energy levels is explained and the ratios δ between the lowest excitation energies, which are related to the electron spin, are determined quantitatively using group theoretical means. The δ are independent of the detailed form of the inter-particle repulsion and of sufficiently larger _s. The obtained δ-values are confirmed by available numerical data. The method is applied to 1D and 2D quantum dots.     

Correlations in quantum dots

The lowest excitations of a repulsively interacting few particle system are investigated within correlated “pocket state” basis functions. For long range interaction and non-isotropic confining potentials the method becomes exact, in the limit of large mean inter-particle distancesr _s. The multiplet structure of the many-electron energy levels is explained and the ratios δ between the lowest excitation energies, which are related to the electron spin, are determined quantitatively using group theoretical means. The δ are independent of the detailed form of the inter-particle repulsion and of sufficiently larger _s. The obtained δ-values are confirmed by available numerical data. The method is applied to 1D and 2D quantum dots.     

Coupled quantum dots as quantum exclusive-OR gate

The concepts relevant to quantum cellular automata and quantum computers are studied using a simple model of a quantum exclusive-OR (QXOR) gate device consisting of four coupled quantum dots. The QXOR device can be charged with up toN = 8 electrons. The quantum bits of the device correspond to states of the device in second quantized form. We use exact diagonalization techniques in the configuration space to calculate physical properties of QXOR as a function of the number of electronsNand external perturbations in the form of electric and magnetic fields. This allows us to investigate the switching of the QXOR gate, and its ability to store and transmit information.     

Asymmetric quantum shot noise in quantum dots

We analyze the frequency-dependent noise of a current through a quantum dot which is coupled to Fermi leads and which is in the Coulomb blockade regime. We show that the asymmetric shot noise, as a function of detection frequency, shows steps and becomes super-Poissonian. This provides experimental access to the quantum fluctuations of the current. We present an exact calculation of the noise for a single dot level and a perturbative evaluation of the noise in Born approximation (sequential tunneling regime but without Markov approximation) for the general case of many levels with charging interaction.     

Towards hybrid circuit quantum electrodynamics with quantum dots

Cavity quantum electrodynamics allows one to study the interaction between light and matter at the most elementary level. The methods developed in this field have taught us how to probe and manipulate individual quantum systems like atoms and superconducting quantum bits with an exquisite accuracy. There is now a strong effort to extend further these methods to other quantum systems, and in particular hybrid quantum dot circuits. This could turn out to be instrumental for a noninvasive study of quantum dot circuits and a realization of scalable spin quantum bit architectures. It could also provide an interesting platform for quantum simulation of simple fermion–boson condensed matter systems. In this short review, we discuss the experimental state of the art for hybrid circuit quantum electrodynamics with quantum dots, and we present a simple theoretical modeling of experiments.     

Enhanced photoluminescence of CdSe quantum dots by the coupling of Ag nanocube and Ag film

The coupling of local surface plasmon(LSP) of nanoparticle and surface plasmon(SP) mode produced by metal film can lead to the enhanced electromagnetic field, which has an important application in enhancing the fluorescence of quantum dots(QDs). Herein, the Ag nanocube and Ag film are used to enhance the fluorescence of CdSe QDs. The enhancement is found to relate to the sizes of the Ag nanocube and the thickness of the Ag film. Moreover, we also present the fluorescence enhancement caused by only SP. The result shows that the coupling between metal nanoparticles and metal film can realize larger field enhancement. Numerical simulation verifies that a nanocube can localize a strong electric field around its corner. All the results indicate that the fluorescence of QDs can be efficiently improved by optimizing the parameters of Ag film and Ag cubes.     

Thermoelectrics with Coulomb-coupled quantum dots

In this article we review the thermoelectric properties of three terminal devices with Coulomb-coupled quantum dots (QDs) as observed in recent experiments [1], [2]. The system we consider consists of two Coulomb-blockade QDs, one of which can exchange electrons with only a single reservoir (heat reservoir), while the other dot is tunnel coupled with two reservoirs at a lower temperature (conductor). The heat reservoir and the conductor interact only via the Coulomb coupling of the quantum dots. It has been found that two regimes have to be considered. In the first one, the heat flow between the two systems is small. In this regime, thermally driven occupation fluctuations of the hot QD modify the transport properties of the conductor system. This leads to an effect called thermal gating. Experiments have shown how this can be used to control charge flow in the conductor by means of temperature in a remote reservoir. We further substantiate the observations with model calculations, and implications for the realisation of an all-thermal transistor are discussed. In the second regime, the heat flow between the two systems is relevant. Here the system works as a nanoscale heat engine, as proposed recently (Sánchez and Büttiker [3]). We review the conceptual idea, its experimental realisation and the novel features arising in this new kind of thermoelectric device such as decoupling of heat and charge flow.     

Magneto-absorption in cylindrical quantum dots

The absorption of light in an ensemble of non-interacting cylindrical quantum dots in the presence of a magnetic field is discussed using a model consisting of dots with rectangular infinitely-high potential barriers. The ensemble’s absorption coefficient is calculated — as well as the threshold frequency of absorption — as a function of the applied magnetic field and the quantum dot size. Theoretical results are compared with experimental data on magneto-luminescence in an In_0.53Ga_0.47As/InP cylindrical quantum dot system. In addition, using a perturbation theory framework, the influence of excitonic effects on the behaviour of the electron-hole energetic spectrum of said system is discussed.     

Photoactivation of silicon quantum dots

We show that free-standing silicon quantum dots (QDs) can be photoactivated by blue or UV optical irradiation. The luminescence intensity increases by an order of magnitude for irradiation times of several minutes under moderate optical power. The cut-off energy for photoactivation is between 2.1 and 2.4 eV, not very different from the activation energy for hydrogen dissociation from bulk silicon surfaces. We propose the mechanism for this effect is associated with silicon-hydride bond breaking and the subsequent oxidation of dangling bonds. This phenomenon could be used to “write” luminescent quantum dots into pre-determined arrays.     

Condensable InP quantum dots solid

Colloidal thioacetic acid-capped InP quantum dots (InP-TAA QDs) and their spin coated-films have been examined in comparison with those of myristic acid-capped InP (InP-MA) QDs. While the QDs are far away from each other in the InP-MA QD films, even in a InP-MA QD film cured at 250 °C, upon thermal annealing a film of InP-TAA QDs at 250 °C, the indium thioacetate groups on the surfaces QDs likely condensed, thus resulting in the QD film that consists of individual and proximally packed InP QDs. The structures of the films of InP-MA QDs or InP-TAA QDs were characterized by means of TEM, XRD, and XPS. The current through the film of InP-TAA QDs cured at 250 °C was about 2–5 orders of magnitude higher than that of the film of InP-MA film annealed by the sample conditions. We, newly in this letter, define this kind of materials architecture as the condensable QDs solid concept.     

Nano-laser on silicon quantum dots

A new conception of nano-laser is proposed in which depending on the size of nano-clusters (silicon quantum dots (QD)), the pumping level of laser can be tuned by the quantum confinement (QC) effect, and the population inversion can be formed between the valence band and the localized states in gap produced from the surface bonds of nano-clusters. Here we report the experimental demonstration of nano-laser on silicon quantum dots fabricated by nanosecond pulse laser. The peaks of stimulated emission are observed at 605 nm and 693 nm. Through the micro-cavity of nano-laser, a full width at half maximum of the peak at 693 nm can reach to 0.5 nm. The theoretical model and the experimental results indicate that it is a necessary condition for setting up nano-laser that the smaller size of QD (d < 3 nm) can make the localized states into band gap. The emission energy of nano-laser will be limited in the range of 1.7-2.3 eV generally due to the position of the localized states in gap, which is in good agreement between the experiments and the theory.     

Valley-based noise-resistant quantum computation using Si quantum dots

We devise a platform for noise-resistant quantum computing using the valley degree of freedom of Si quantum dots. The qubit is encoded in two polarized (1,1) spin-triplet states with different valley compositions in a double quantum dot, with a Zeeman field enabling unambiguous initialization. A top gate gives a difference in the valley splitting between the dots, allowing controllable interdot tunneling between opposite valley eigenstates, which enables one-qubit rotations. Two-qubit operations rely on a stripline resonator, and readout on charge sensing. Sensitivity to charge and spin fluctuations is determined by intervalley processes and is greatly reduced as compared to conventional spin and charge qubits. We describe a valley echo for further noise suppression.