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Author: Jason Leonard Publisher: 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.
Author: Jason Leonard Publisher: 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.
Author: Yuliya Yevgenyevna Kuznetsova Publisher: 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.
Author: Joe Wilkes Publisher: 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.
Author: Aaron Tynes Hammack Publisher: 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.
Author: Jason R. Leonard Publisher: 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.
Author: Matthew W. Hasling Publisher: ISBN: Category : Languages : en Pages : 62
Book Description
Indirect excitons are bosonic quasiparticles composed of an electron and a hole confined to spatially separated quantum wells. Many properties of excitons, such as their low effective mass, long lifetime, tunable energy, and optically active nature, make them an ideal system for studying condensed matter phenomena. This dissertation explores the transport properties associated with indirect excitons in various environments. In this dissertation, exciton transport is studied in multiple devices, created by carefully patterned electrodes, which create a varied potential energy landscape for the excitons. The first device is used to trap large amounts of excitons, which can be used to study the properties of dense exciton gases. The second device is used as a stirring potential for indirect excitons, and can give excitons angular momentum while they collect to the center of the device. In addition, a record high quality single quantum well structure is characterized, which may prove to be a new platform for studying indirect excitons. Measurements of this new sample show large transport and a record high diffusion coefficient for indirect excitons.
Author: Chelsey Dorow Publisher: ISBN: Category : Languages : en Pages : 71
Book Description
Over several decades, research in semiconductor physics has revealed a rich plethora of physical phenomena filled with electric, magnetic, and optical processes for physicists and engineers to observe and manipulate. In addition to hosting a number of fundamental discoveries in physics, several of which merited Nobel Prizes, semiconductor physics has also revolutionized modern technology, most notably in the field of computing. An especially interesting topic in this field is the physics of quasiparticles, which are excitations or disturbances in matter that resemble particles in free space. This dissertation focuses on excitons, which are quasiparticles that exist in semiconductor materials and are a bound state of an electron and a hole. Excitons can interact with light, either through their photo-generation or by radiative recombination of the electron and hole, and therefore can aid in the study of the interaction of light and matter. This dissertation in particular looks at a specially engineered system of excitons: indirect excitons in coupled quantum wells. In this system, the electron and hole of the exciton are confined to two separate quantum well layers and are as a result separated in space, typically by ∼ 10 nm, depending on the coupled quantum well structure. Indirect excitons possess several unique properties including a built-in electric dipole moment, long lifetimes, energy control by applied voltage, and the ability to form a quantum Bose gas, making them a useful system to study fundamental physics of cold bosons and to investigate ways to integrate these properties into modern day technology. The experiments detailed in this dissertation probe the basic physics of exciton transport in high magnetic fields and expand upon our current understanding of how nano-scale devices can be used to control electronic and optical processes in solids.
Author: Jason Leonard
Author: Jason Leonard
Author: Yuliya Yevgenyevna Kuznetsova
Author: Joe Wilkes
Author: Aaron Tynes Hammack
Author: Jason R. Leonard
Author: Chih-Wei Eddy Lai
Author: Matthew W. Hasling
Author: Chelsey Dorow
Author: Smadar Ben-Tabou de-Leon
Author: Leonidas Mouchliadis