Author: Chih-Wei Eddy LaiPublisher:
ISBN:
Category :
Languages : en
Pages : 362
Book Description
Spatially Indirect Excitons in Coupled Quantum Wells
Author: Chih-Wei Eddy LaiFinal Report, DOE Grant DE-FG02-99ER45780, "Indirect Excitons in Coupled Quantum Wells."
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 9
Book Description
The is the final technical report for this project, which was funded by the DOE from 1999 to 2012. The project focused on experimental studies of spatially indirect excitons in coupled quantum wells, with the aim of understanding the quantum physics of these particles, including such effects as pattern formation due to electron-hole charge separation, the Mott plasma-insulator transition, luminescence up-conversion through field-assisted tunneling, luminescence line shifts due to many-body renormalization and magnetic field effects on tunneling, and proposed effects such as Bose-Einstein condensation of indirect excitons and phase separation of bright and dark indirect excitons. Significant results are summarized here and the relation to other work is discussed.
Exciton Transport Phenomena in GaAs Coupled Quantum Wells
Author: Jason LeonardPublisher: Springer
ISBN: 3319697331
Category : Technology & Engineering
Languages : en
Pages : 67
Book Description
This thesis presents results crucial to the emerging field of indirect excitons. These specially designed quasiparticles give the unique opportunity to study fundamental properties of quantum degenerate Bose gases in semiconductors. Furthermore, indirect excitons allow for the creation of novel optoelectronic devices where excitons are used in place of electrons. Excitonic devices are explored for the development of advanced signal processing seamlessly coupled with optical communication. The thesis presents and describes the author's imaging experiments that led to the discovery of spin transport of excitons. The many firsts presented herein include the first studies of an excitonic conveyer, leading to the discovery of the dynamical localization-delocalization transition for excitons, and the first excitonic ramp and excitonic diode with no energy-dissipating voltage gradient.
Transport of Indirect Excitons in Coupled Quantum Wells
Author: Yuliya Yevgenyevna KuznetsovaPublisher:
ISBN: 9781321451900
Category :
Languages : en
Pages : 67
Book Description
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.
Hydrodynamics of Indirect Excitons in Coupled Quantum Wells
Author: Joe WilkesPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
This thesis comprises a theoretical study of the dynamics of indirect excitons in coupled quantum wells at low lattice temperatures. The results of numerical simulations of the exciton photoluminescence pattern are presented and compared to available experimental data. The in-plane transport of quantum well excitons created by laser excitation is modeled using a non-linear drift-diffusion equation. Combined with a model of exciton relaxation thermodynamics, a complete description of the evolution of the exciton density and temperature is built. The optical decay of indirect excitons is included in the modeling. This is used to make predictions of the spatial photoluminescence patterns which have been observed experimentally. The transport of dipole orientated excitons via externally applied electrostatic potentials is also studied. The drift-diffusion equation is adapted to include the inplane electric field. This is done for some specific forms of the potential landscapes such as a linear potential energy gradient and a propagating lattice. These correspond to some recent experiments for which results are available. The combined theoretical and experimental studies reveal a deeper insight into the transport properties of indirect excitons. Finally, the external ring structure in the indirect exciton emission pattern is studied. Its formation is modeled using a set of coupled transport equations for electrons, holes and indirect excitons. The Coulomb interactions between all three species are incorporated in the model. It is shown that these interactions lead to an instability in the external ring and are responsible for its fragmentation into a periodic array of islands which has been observed experimentally.
Exciton Transport Phenomena in GaAs Coupled Quantum Wells
Author: Jason R. LeonardPublisher:
ISBN:
Category :
Languages : en
Pages : 83
Book Description
In GaAs excitons are optically active making them ideally suitable for optical communications and computation. An exciton is composite particle composed of an electron and hole. Indirect excitons are excitons with the electron and hole spatially separated into different quantum wells. Indirect excitons are oriented in the same direction allowing indirect excitons to be manipulated by voltage gradients. This dissertation explores controlling exciton transport with ramps--shaped electrodes that operate as excitonic diodes, or in a crossed ramp configuration operate as an optically controlled transistor. This dissertation also demonstrates an exciton conveyer--a moving lattice created by electrodes driven with AC voltages--that transports excitons over large distances. This dissertation concludes with an observation of exciton spin transport.
Studies of Transport and Thermalization of Excitons and the Development of Techniques for In-situ Manipulation of Excitons in Coupled Quantum Wells
Author: Aaron Tynes HammackPublisher:
ISBN: 9781109764604
Category :
Languages : en
Pages : 168
Book Description
The study of excitons in semiconductors is a rich field that has seen numerous beautiful developments during the seven decades since they were proposed by Frenkel [1931]. The exciton states in dielectric materials and molecular complexes are fundamental to understanding the full electronic structure of materials and the complex interactions between light and matter. Of particular interest is the fact that excitons, bound electron-hole pairs, form composite bosons with very low effective masses. This opens up an incredibly rich opportunity to study the phase space of quantum degenerate Bose gases at relatively high temperatures. An overview of many of the rich features that have been observed in exciton gases is presented. The system of indirect excitons in coupled quantum wells (CQWs) provides for drastically increased and tunable exciton lifetimes, leading to improved thermalization. The present experimental study presents a full steady state and dynamic model for the transport, generation, recombination, and thermalization of indirect excitons in CQWs, as well as methods for in-situ manipulation of indirect excitons by both optical and electrical methods. Both the optical and electrical methods for exciton control provide for dynamic manipulation of excitons on timescales significantly shorter than the lifetimes of indirect excitons.
Thermalization, Diffusion and Photoluminescence of Statistically-degenerate Indirect Excitons in Coupled Quantum Wells
Author: Lois Elenid SmallwoodPublisher:
ISBN:
Category : Electrons
Languages : en
Pages : 120
Book Description
Quantum Systems of Indirect Excitons in GaAs Heterostructures
Author: Darius Jamsheed ChoksyPublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Semiconductors have proven themselves to be an excellent platform for both the development of new technologies and the study of fundamental physics. Various semiconductor materials provide us the ability to control and study the bulk system behavior, electronic behavior, and light matter interactions. Of particular interest to this paper is the study of a quasi-particle that can form in semiconductors known as an exciton. Made from an electron and hole, it also has very useful photonic properties. In our work we study excitons created by photoexcitation, where a laser excites an electron from the lattice, creating an electron and hole, the electrons and holes created can then form a bound state known as an exciton. Excitons can transform into photons via radiative recombination. Our experiments typically deal with a system of quantum wells, engineered to keep the electrons and holes spatially separated, a bound pair of an electron and hole with the electron and hole in different quantum wells is known as an indirect exciton. Some of the properties of indirect excitons are an electric dipole moment, energy controlled by voltage, long lifetimes, macroscopic transport, and they are bosons. These properties as well as their interaction with light allow for systems to be created that act as proof-of-concept prototypes for excitonic devices, as well as a platform to study fundamental physics of cold bosons. The work in this dissertation is primarily focused on dipole-dipole attraction and the formation of a Fermi edge singularity in these systems. These works give us new insights into the interactions of bosons and formation of new states of matter.
Author: Sang Yup Kim