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Luminescence Anomaly Of Two Dimensional Excitons In Gaas Coupled Quantum Wells
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Book Synopsis Luminescence Anomaly of Two-Dimensional Excitons in GaAs Coupled Quantum Wells by : T. Fukuzawa
Download or read book Luminescence Anomaly of Two-Dimensional Excitons in GaAs Coupled Quantum Wells written by T. Fukuzawa and published by . This book was released on 1992 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt: The possibility of a phase transition into an ordered state in a two-dimensional (2D) system of spatially separated electron-hole pairs has been suggested by Lozovik and Yudson and Shevchenko independently. Their proposal has recently been extended by Fukuzawa to a system formed by two GaAs/AlGaAs coupled quantum wells subject to an electric field. The long exciton lifetimes that can be achieved in such a semiconductor heterostructure, as well as the small Coulomb screening due to the interaction between oriented dipoles, make it particularly suitable for the study of phase transitions, be it like the one proposed by Lozovik and Yudson, and Shevchenko, or a Kosterliz-Thouless transition of a neutral Coulomb gas. The photoluminescence (PL) of GaAs-GaO. 7A10.3As structures consisting of two 50A quantum wells separated by a 40A barrier has shown a dramatic temperature dependence when an electric field is applied perpendicular to the well interfaces. The polarization of carriers and the energy shifts induced by the field lead to a PL spectrum consisting of two distinct peaks, one of which is associated with spatially direct interband transitions and another, much more intense, that involves spatially-separated electrons and holes (type-11 exciton).
Book Synopsis Excitons in Coupled Double Quantum Wells by : Sang Yup Kim
Download or read book Excitons in Coupled Double Quantum Wells written by Sang Yup Kim and published by . This book was released on 2001 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Government Reports Annual Index by :
Download or read book Government Reports Annual Index written by and published by . This book was released on 1992 with total page 1128 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Spatially Indirect Excitons in Coupled Quantum Wells by :
Download or read book Spatially Indirect Excitons in Coupled Quantum Wells written by and published by . This book was released on 2004 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt: Microscopic quantum phenomena such as interference or phase coherence between different quantum states are rarely manifest in macroscopic systems due to a lack of significant correlation between different states. An exciton system is one candidate for observation of possible quantum collective effects. In the dilute limit, excitons in semiconductors behave as bosons and are expected to undergo Bose-Einstein condensation (BEC) at a temperature several orders of magnitude higher than for atomic BEC because of their light mass. Furthermore, well-developed modern semiconductor technologies offer flexible manipulations of an exciton system. Realization of BEC in solid-state systems can thus provide new opportunities for macroscopic quantum coherence research. In semiconductor coupled quantum wells (CQW) under across-well static electric field, excitons exist as separately confined electron-hole pairs. These spatially indirect excitons exhibit a radiative recombination time much longer than their thermal relaxation time a unique feature in direct band gap semiconductor based structures. Their mutual repulsive dipole interaction further stabilizes the exciton system at low temperature and screens in-plane disorder more effectively. All these features make indirect excitons in CQW a promising system to search for quantum collective effects. Properties of indirect excitons in CQW have been analyzed and investigated extensively. The experimental results based on time-integrated or time-resolved spatially-resolved photoluminescence (PL) spectroscopy and imaging are reported in two categories. (i) Generic indirect exciton systems: general properties of indirect excitons such as the dependence of exciton energy and lifetime on electric fields and densities were examined. (ii) Quasi-two-dimensional confined exciton systems: highly statistically degenerate exciton systems containing more than tens of thousands of excitons within areas as small as (10 micrometer)2 were observed. The spatial and energy distributions of optically active excitons were used as thermodynamic quantities to construct a phase diagram of the exciton system, demonstrating the existence of distinct phases. Optical and electrical properties of the CQW sample were examined thoroughly to provide deeper understanding of the formation mechanisms of these cold exciton systems. These insights offer new strategies for producing cold exciton systems, which may lead to opportunities for the realization of BEC in solid-state systems.
Book Synopsis High Density Excitonic State in Two-Dimensional Multiquantum Wells by : H. Q. Le
Download or read book High Density Excitonic State in Two-Dimensional Multiquantum Wells written by H. Q. Le and published by . This book was released on 1984 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt: A sharp photoluminescence spectral feature has been observed in AlGaAs. GaAs multi-quantum-well structures under high intensity, resonant excitation at the ground state exciton. This feature, which appears below the exciton ground state, emerges from a cold dense system of excitons, but prior to the break-up of excitons into an electron-hole plasma. A collective excitonic state is speculated.
Book Synopsis Government Reports Announcements & Index by :
Download or read book Government Reports Announcements & Index written by and published by . This book was released on 1992 with total page 778 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Indirect Excitons in GaAs Coupled Quantum Wells by : Alexander Arthur High
Download or read book Indirect Excitons in GaAs Coupled Quantum Wells written by Alexander Arthur High and published by . This book was released on 2012 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt: Indirect excitons in coupled quantum wells form a unique system for both development of novel optoelectronic devices as well as studies of the low temperature physics of bosons in condensed matter systems. An exciton is a quasiparticle which is a bound state of an electron and hole. Excitons can be created by light, and when they recombine they can emit light. In an indirect exciton, the electron and hole are spatially separated, which results in a long exciton lifetime as well as an electronic dipole moment. The long lifetime allows excitons to travel over large distances ~ 100[mu]m. The electronic dipole moment allows direct electronic control of the exciton energy. Therefore, as an optical media that is also electronically controllable, indirect excitons offer promise for development of new, efficient optoelectronic devices. In this dissertation, we prototype two new optoelectronic devices based on indirect excitons : the exciton optoelectronic transistor, and the excitonic integrated circuit. In addition, the long radiative lifetime allows indirect excitons to cool to very low temperatures below the temperature of quantum degeneracy. Traps are of particular interest for studies of low temperature gases, as they facilitate creation of high density, cold gases as well as offer opportunities for in situ control of the gas. This dissertation presents novel, precisely engineered trapping potentials for exciton gases based on electronic control and makes a thorough examination of the physical properties of the trapped gas. Furthermore, as a bosonic quasiparticle, excitons can be expected to form a condensate under certain density and temperature conditions. A signature of condensation is the emergence of spontaneous extended coherence, where the coherence length significantly exceeds its classically expected value. We present the first evidence for extended spatial coherence in an exciton system - the system of exciton rings. A pattern of extended spontaneous coherence is correlated with a pattern of spontaneous polarization, revealing the properties of a multicomponent coherent state. We also observed phase singularities in the coherent exciton gas. Lastly, we probe the spatial coherence of excitons in an electrostatic trap and present direct evidence for Bose-Einstein condensation of excitons therein.
Download or read book Chemical Abstracts written by and published by . This book was released on 2002 with total page 2540 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Spatially Indirect Excitons in Coupled Quantum Wells by : Chih-Wei Eddy Lai
Download or read book Spatially Indirect Excitons in Coupled Quantum Wells written by Chih-Wei Eddy Lai and published by . This book was released on 2004 with total page 362 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Strong Light-matter Coupling in Microcavity-embedded Semiconductor Quantum Wells and Quantum Dots by : Kanchana Sivalertporn
Download or read book Strong Light-matter Coupling in Microcavity-embedded Semiconductor Quantum Wells and Quantum Dots written by Kanchana Sivalertporn and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis presents a theoretical investigation of exciton polaritons in strongly-coupled exciton-photon microcavity systems. Two different systems, a coupled quantum well (CQW) embedded in a planar microcavity and a quantum dot (QD) inside a micropillar cavity, are studied using suitable theoretical models. The exciton-polariton states are calculated and their optical properties are investigated in detail, showing a good agreement with experimental observations. For a CQW structure, the excitonic states in the presence of the electric field applied in the growth direction are calculated by solving the Schrodinger equation in real space. The field dependence of exciton transition energy, binding energy, oscillator strength, lifetime and absorption is studied. The exciton ground state experiences a crossover from direct to indirect state at low electric field. A single state-basis calculation in which only the electron and hole ground states are taken into account is also made and compared with the full accurate calculation model. The polariton effect in a microcavity-embedded CQW is investigated based on the semiclassical theory. The light-matter interaction is treated by solving coupled material and Maxwell's equations. The reflectivity and absorption spectra are calculated for different detunings using the scattering matrix method. When a cavity mode is tuned to an exciton mode (zero detuning), an anticrossing of two polariton modes is observed, showing that the system is in the strong coupling regime. In addition, the fractions of direct exciton, indirect exciton and cavity modes contributed to the polariton states are calculated using the microscopic theory. The resulting polariton state with comparable contributions ofall three components called dipolariton is observed. Finally, the dynamics of the strongly-coupled exciton-cavity system in the QD-micropillar system is studied using the four wave mixing (FWM) theory applied to the Jaynes-Cummings model. Spectrally resolved and time-resolved FWM signals are calculated for different temperatures. Temperature plays the role of the parameter controlling the detuning. The beat periods of the first and second rungs of the JC ladder are also investigated, showing that the second rung has a sqaure- shorter period compared to the beat period of the first rung. To reveal the coherent coupling between two distant QDs, the FWM signals are Fourier-transformed into a two-dimensional frequency domain. It is found that the off-diagonal components in these 2D spectra are nonzero, demonstrating the coherent coupling between isolated QDs. In addition, the phase correction is developed. This procedure is neccessary for a comparison with the experiment which has random phases for different detunings. A quantitative agreement between the prediction and measurement is achieved and demonstrated.
Book Synopsis Il Nuovo Cimento Della Società Italiana Di Fisica by :
Download or read book Il Nuovo Cimento Della Società Italiana Di Fisica written by and published by . This book was released on 1995 with total page 806 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Tableaux anciens des XVIIe-XVIIIe et XIX e siècles objets d'art et de très bel ameublement, tapisseries tapis d'Orient by :
Download or read book Tableaux anciens des XVIIe-XVIIIe et XIX e siècles objets d'art et de très bel ameublement, tapisseries tapis d'Orient written by and published by . This book was released on 1990 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Photoluminescence Study of a Dilute Two-dimensional Electron Gas in GaAs/AlGaAs Quantum Wells by : Gail L. Waytena
Download or read book Photoluminescence Study of a Dilute Two-dimensional Electron Gas in GaAs/AlGaAs Quantum Wells written by Gail L. Waytena and published by . This book was released on 1987 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Exciton Transport and Thermodynamics in Gallium Arsenide Quantum Wells by : Howard Wuk Yoon
Download or read book Exciton Transport and Thermodynamics in Gallium Arsenide Quantum Wells written by Howard Wuk Yoon and published by . This book was released on 1994 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis describes the use of optical absorption and photoluminescence spectroscopy in understanding the spatial transport and energy relaxation of excitons in quantum well systems. I discuss the mechanism of carrier-induced changes in the absorption spectrum of a 210A GaAs multiple quantum well, and show that at moderate densities, the enhanced transmission at the heavy-hole exciton energy is due to collision broadening. I also discuss the time dependent and excitation-energy dependent energy shifts of the heavy-hole exciton. I use the changes induced in the absorption spectra due to the presence of carriers as a probe for measuring the spatial transport, and I describe the transport using an ionized-impurity scattering model. I also measure the carrier temperatures from the high energy slopes of the time-resolved photoluminescence spectra, and describe the roles of the carrier temperatures and carrier expansion on the time dynamics of the exciton luminescence intensity. In the last chapter, I study the transport properties of excitons in an asymmetric-coupled quantum well system, and explain the experimental results with a model based on interface-roughness scattering.
Book Synopsis Condensation of Quasi-two-dimensional Biexcitons in a Single Heterojunction Quantum Well by :
Download or read book Condensation of Quasi-two-dimensional Biexcitons in a Single Heterojunction Quantum Well written by and published by . This book was released on 1999 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt: Excitons that coexist with a degenerate two-dimensional electron gas in the same quantum well subband have been observed in the photoluminescence from the recombination of electrons with localized photoexcited holes, At a critical electron density, an abrupt decrease in the exciton radiative recombination rate is observed, along with the formation of biexcitons. With increased excitation intensity, photoluminescence spectra are observed that verify theory on the radiative renormalization of biexcitons and strongly indicate the occurrence of a Bose-Einstein condensation of biexcitons.
Download or read book Physics Briefs written by and published by . This book was released on 1994 with total page 1224 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Transport of Indirect Excitons in Coupled Quantum Wells by : Yuliya Yevgenyevna Kuznetsova
Download or read book Transport of Indirect Excitons in Coupled Quantum Wells written by Yuliya Yevgenyevna Kuznetsova and published by . This book was released on 2014 with total page 67 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation explores studies of transport of indirect excitons (bosonic quasiparticles composed of bound pairs of an electron and a hole confined to spatially separated layers) in GaAs coupled quantum wells. The small mass and long lifetime of indirect excitons result in a relatively high quantum degeneracy temperature and efficient cooling, making indirect excitons a model system for studies of physics of cold bosons. In addition, indirect excitons are optically active, electronically controllable and have long enough lifetimes that their transport distances can be accommodated by lithography. These properties make indirect excitons a promising system for creating excitonic devices. The direction of the research presented in this dissertation is thus twofold: studying fundamental physics of excitons, including transport, thermalization, coherence, spin currents, and properties in high magnetic fields, and realization of optical excitonic devices, such as traps and transistors.
