Aharonov-Bohm interference in quantum ring exciton: effects of built-in electric fields

We report a comprehensive discussion of quantum interference effects due to the finite structure of excitons in quantum rings and their first experimental corroboration observed in the optical recombinations. Anomalous features that appear in the experiments are analyzed according to theoretical models that describe the modulation of the interference pattern by temperature and built-in electric fields.Comment: 6 pages, 7 figure

МОДЕЛИРОВАНИЕ РЕЖИМОВ РАБОТЫ СУДОВЫХ ПОТРЕБИТЕЛЕЙ ЭЛЕКТРОЭНЕРГИИ С ИСПОЛЬЗОВАНИЕМ ДИАГРАММ СОСТОЯНИЙ

The simulation of operational modes of autonomous power system electrical loads for composition of loads and generators patterns, which can be used for load forecast algorithms verification and energy efficiency of the system estimation, is discussed. The probabilistic automata using for simulation of technological processes in the system and of loads commutations processes was revealed to be able to represent correlation between the loads. The model of the power system, consisting of the interdependent parallel automata network, the signal conditioning block and the generators management block and having the communication links with the database for simulation results processing, is proposed. References 8, figures 4.Рассмотрено имитационное моделирование работы потребителей электроэнергии в автономных электроэнергетических установках с целью получения суточных графиков нагрузки установки и режимов работы генераторных агрегатов, которые могут быть использованы для верификации алгоритмов прогнозирования нагрузки и расчета показателей энергоэффективности установки. Предложено использование вероятностных автоматов для моделирования процессов, обуславливающих характеристики режимов работы потребителей электроэнергии, и процессов коммутации потребителей, что позволит учесть корреляционные связи между режимами их работы. Приведено модель электроэнергетической установки, состоящей из сети параллельных взаимозависимых автоматов, блоков нормализации сигналов и управления режимами работы генераторных агрегатов и имеющей возможность коммуникации с системой управления базами данных для хранения полученных в результате моделирования данных. Библ. 8, рис. 4.Розглянуто імітаційне моделювання роботи споживачів електроенергії в автономних електроенергетичних установках з метою отримання добових графіків навантаження установки та режимів роботи генеруючих агрегатів, які можуть бути використані для веріфікації алгоритмів прогнозування навантаження та розрахунку покажчиків енергоефективності установки. Запропоновано використання ймовірнісних автоматів для моделювання процесів, що обумовлюють характеристики режимів роботи споживачів, та процесів комутації споживачів, що дозволить врахувати кореляційні зв’язки між режимами їх роботи. Наведено модель електроенергетичної установки, яка складається з мережи паралельних взаємопов’язаних автоматів, блоків нормалізації сигналів та керування режимами роботи генеруючих агрегатів та яка має засоби комунікації з системою керування базами даних для збереження отриманих в результаті моделювання даних. Бібл. 8, рис. 4

Influence of Si doping on InAs/GaAs quantum dot solar cells with AlAs cap layers

A novel all-optical forward-viewing photoacoustic probe using a flexible coherent fibre-optic bundle and a Fabry- Perot (FP) ultrasound sensor has been developed. The fibre bundle, along with the FP sensor at its distal end, synthesizes a high density 2D array of wideband ultrasound detectors. Photoacoustic waves arriving at the sensor are spatially mapped by optically scanning the proximal end face of the bundle in 2D with a CW wavelength-tunable interrogation laser. 3D images are formed from the detected signals using a time-reversal image reconstruction algorithm. The system has been characterized in terms of its PSF, noise-equivalent pressure and field of view. Finally, the high resolution 3D imaging capability has been demonstrated using arbitrary shaped phantoms and duck embryo

Si-Doped InAs/GaAs Quantum-Dot Solar Cell With AlAs Cap Layers

One of the requirements for strong subbandgap photon absorption in the quantum-dot intermediate-band solar cell (QD-IBSC) is the partial filling of the intermediate band. Studies have shown that the partial filling of the intermediate band can be achieved by introducing Si doping to the QDs. However, the existence of too many Si dopants leads to the formation of point defects and, hence, a reduction of photocurrent. In this study, the effect of Si doping on InAs/GaAs QD solar cells with AlAs cap layers is studied. The AlAs cap layers prevent the formation of the wetting layer during QD growth and reduce the Si doping density needed to achieve QD state filling. Furthermore, the passivation of defect states in the QD with moderate Si doping is demonstrated, which leads to an enhancement of the carrier lifetime in the QDs and, hence, the open-circuit voltage

1.3-μm InAs/GaAs quantum-dot laser monolithically grown on Si Substrates operating over 100°C

A high-performance 1.3 μm InAs/GaAs quantum-dot laser directly grown on Si substrates has been achieved by using InAlAs/GaAs strained-layer superlattice serving as dislocation filter layers (DFLs). The Si-based laser achieves lasing operation up to 111°C with a threshold current density of 200 A/cm 2 and an output power exceeding 100 mW at room temperature

Effect of dimensionality and morphology on polarized photoluminescence in quantum dot-chain structures

Change of the photoluminescence (PL) polarization is studied by changing the excitation intensity and temperature for aligned In(Ga)As quantum dot (QD) structures with varying inter-dot distances grown by molecular beam epitaxy on semi-insulating GaAs (100) substrates. An unusual increase of the polarization ratio is observed by increasing the temperature and/or excitation intensity throughout a low temperature (T < 70 K) and low intensity ('I IND. ex' < 1 W/'cm POT. 2') range. This increase as well as the general behavior of the polarized PL are the results of the exciton dynamics and the peculiarities of the system morphology. They are due to the varying inter-dot distances which change the system from zero-dimensional comprised of isolated QDs to one-dimensional comprised of wire-like structures

Raman scattering reveals strong LO-phonon-hole-plasmon coupling in nominally undoped GaAsBi: optical determination of carrier concentration

We report room-temperature Raman scattering studies of nominally undoped (100) GaAs1−xBix epitaxial layers exhibiting Biinduced (p-type) longitudinal-optical-plasmon coupled (LOPC) modes for 0.018≤x≤0.048. Redshifts in the GaAs-like optical modes due to alloying are evaluated and are paralleled by strong damping of the LOPC. The relative integrated Raman intensities of LO(Γ) and LOPC ALO/ALOPC are characteristic of heavily doped p-GaAs, with a remarkable near total screening of the LO(Γ) phonon (ALO/ALOPC →0) for larger Bi concentrations. A method of spectral analysis is set out which yields estimates of hole concentrations in excess of 5 × 1017 cm−3 and correlates with the Bi molar fraction. These findings are in general agreement with recent electrical transport measurements performed on the alloy, and while the absolute size of the hole concentrations differ, likely origins for the discrepancy are discussed. We conclude that the damped LO-phonon-hole-plasmon coupling phenomena plays a dominant role in Raman scattering from unpassivated nominally undoped GaAsBi

Mechanism of periodic height variations along self-aligned VLS-grown planar nanostructures

In this study we report in-plane nanotracks produced by molecular-beam-epitaxy (MBE) exhibiting lateral self-assembly and unusual periodic and out-of-phase height variations across their growth axes. The nanotracks are synthesized using bismuth segregation on the GaAsBi epitaxial surface, which results in metallic liquid droplets capable of catalyzing GaAsBi nanotrack growth via the vapor–liquid–solid (VLS) mechanism. A detailed examination of the nanotrack morphologies is carried out employing a combination of scanning electron and atomic force microscopy and, based on the findings, a geometric model of nanotrack growth during MBE is developed. Our results indicate diffusion and shadowing effects play significant roles in defining the interesting nanotrack shape. The unique periodicity of our lateral nanotracks originates from a rotating nucleation “hot spot” at the edge of the liquid–solid interface, a feature caused by the relative periodic circling of the non-normal ion beam flux incident on the sample surface, inside the MBE chamber. We point out that such a concept is divergent from current models of crawling mode growth kinetics and conclude that these effects may be utilized in the design and assembly of planar nanostructures with controlled non-monotonous structure

Cooperative Effects in the Photoluminescence of (In,Ga)As/GaAs Quantum Dot Chain Structures

Multilayer In0.4Ga0.6As/GaAs quantum dot (QD) chain samples are investigated by means of cw and time-resolved photoluminescence (PL) spectroscopy in order to study the peculiarities of interdot coupling in such nanostructures. The temperature dependence of the PL has revealed details of the confinement. Non-thermal carrier distribution through in-chain, interdot wave function coupling is found. The peculiar dependences of the PL decay time on the excitation and detection energies are ascribed to the electronic interdot coupling and the long-range coupling through the radiation field. It is shown that the dependence of the PL decay time on the excitation wavelength is a result of the superradiance effect