Transport of Indirect Excitons in GaAs Heterostructures

Transport of Indirect Excitons in GaAs Heterostructures
Author: Matthew W. Hasling
Publisher:
Total Pages: 62
Release: 2018
Genre:
ISBN:

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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.

Quantum Systems of Indirect Excitons in GaAs Heterostructures

Quantum Systems of Indirect Excitons in GaAs Heterostructures
Author: Darius Jamsheed Choksy
Publisher:
Total Pages: 0
Release: 2023
Genre:
ISBN:

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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.

Indirect Exciton Propagation in Van Der Waals Heterostructures

Indirect Exciton Propagation in Van Der Waals Heterostructures
Author: Lewis H. Fowler-Gerace
Publisher:
Total Pages: 0
Release: 2022
Genre:
ISBN:

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Spatially indirect excitons (IXs), also known as interlayer excitons, are bound pairs of an electron and a hole in spatially separated layers. IXs can propagate over long distances before they recombine into light, and they can cool down below the temperature of quantum degeneracy within their lifetimes, which can be controlled by gate voltage up to microseconds and beyond. These properties make IXs a promising platform for studying fundamental physics phenomena and as the medium for highly efficient signal processing devices. IXs were originally studied in gallium arsenide (GaAs) heterostructures, where IXs have shown evidence for Bose-Einstein condensation, and proof of principle has been demonstrated for excitonic transistors and excitonic integrated circuits. IXs only exist at low temperatures in GaAs systems due to the low IX binding energy on the order of 10 meV. In the transition-metal dichalcogenide (TMD) heterostructure system, the IX binding energy is predicted to be more than two orders of magnitude higher, making IXs stable at room temperature and allowing for the possibility of high temperature IX superfluidity. To date, observation of some of the key IX behaviors, namely the long-range IX transport and evidence of IX condensation, has remained elusive in the TMD system. This dissertation characterizes the IX spectrum in a MoSe2/WSe2 heterostructure, demonstrates the realization and control of long-range IX propagation using a new mechanism beyond the know mechanism for IX control in GaAs heterostructures, and separately identifies a quantum origin for the propagation of IXs generated by resonant excitation in the TMD heterostructure.

Exciton Transport Phenomena in GaAs Coupled Quantum Wells

Exciton Transport Phenomena in GaAs Coupled Quantum Wells
Author: Jason R. Leonard
Publisher:
Total Pages: 83
Release: 2016
Genre:
ISBN:

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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.

2D Excitonic Materials and Devices

2D Excitonic Materials and Devices
Author:
Publisher: Elsevier
Total Pages: 270
Release: 2023-11-23
Genre: Science
ISBN: 0443193932

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Semiconductors and Semimetals series, highlights new advances in the field, with this new volume presenting interesting chapters. Each chapter is written by an international board of authors. Provides the latest information on cancer research Offers outstanding and original reviews on a range of cancer research topics Serves as an indispensable reference for researchers and students alike

Subnanosecond Control of Excitons in Coupled Quantum Well Nanostructures

Subnanosecond Control of Excitons in Coupled Quantum Well Nanostructures
Author: Alexander Graham Winbow
Publisher:
Total Pages: 280
Release: 2010
Genre:
ISBN: 9781124378299

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Indirect excitons in GaAs coupled quantum well nanostructures are a versatile system for fundamental study of cold neutral bosonic gases and demonstration of novel optoelectronic devices based on excitons -- a bound electron-hole pair -- rather than electrons. Indirect exciton lifetimes range from nanoseconds to microseconds and cool rapidly after photoexcitation to the lattice temperature. Lithographically-patterned electrodes enable design of potential energy landscapes, and both energy and lifetime can be controlled in situ, rapidly, on timescales much shorter than the exciton lifetime. Such intrinsically optoelectronic devices can operate at speeds relevant to optical networks, and later be fabricated in other semiconductors for higher-temperature operation. Two different kinds of devices are demonstrated Photon storage -- an optical memory -- with 250 ps rise time of the readout optical signal and storage time reaching microseconds was implemented with indirect excitons in CQW. The storage and release of photons was controlled by the gate voltage pulse, and the transient processes in the CQW studied by measuring the kinetics of the exciton emission spectra. This control of excitons on timescales much shorter than the exciton lifetime demonstrates the feasibility of studying excitons in in situ controlled electrostatic traps. The Exciton Conveyer is a laterally moving electrostatic lattice potential for actively transporting excitons. Generated by laterally modulated electrodes, the potential velocity and depth are controlled in situ by frequency and voltage. We observed exciton transport characterized by average exciton cloud spatial extension over several tens of microns, and observed dynamical localization-delocalization transitions for the excitons in the conveyer : In the localization regime of deeper potentials and moderate exciton density, excitons are moved by the conveyer; in the delocalized regime of shallower lattice potential or high exciton density, excitons do not follow the conveyer motion. We explore conveyer velocities both slower and faster than phonon velocities. Realizing subnanosecond manipulations of exciton energy and lifetime required versatile control of pulsed and multiple AC RF electrical signals in optical, liquid helium cryogenic systems. Considerable detail is presented of design, construction, and test of flexible experimental apparatus.

Chemical Abstracts

Chemical Abstracts
Author:
Publisher:
Total Pages: 2540
Release: 2002
Genre: Chemistry
ISBN:

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