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Photon-Assisted Transmission through a Double-Barrier Structure

Description: The authors study multi-photon-assisted transmission of electrons through single-step, single-barrier and double-barrier potential-energy structures as a function of the photon energy and the temperature. Sharp resonances in the spectra of the tunneling current through double-barrier structures are relevant to infra-red detectors.
Date: June 27, 2000
Creator: LYO,SUNGKWUN K.
Partner: UNT Libraries Government Documents Department

Real-space and energy representations for the interface roughness scattering in quantum-well structures

Description: The authors show that the real space representation of the interface-roughness as a fluctuating potential in the coordinate space is equivalent to the usual energy-fluctuation representation for intrasublevel scattering in a single quantum well with a generally shaped confinement-potential profile. The coordinate picture is, however, more general and can be used for higher-order effects and multi-sublevel scattering in coupled multi-quantum-well structures.
Date: April 24, 2000
Creator: LYO,SUNGKWUN K.
Partner: UNT Libraries Government Documents Department

Energy Transfer of Excitons Between Quantum Wells Separated by a Wide Barrier

Description: We present a microscopic theory of the excitonic Stokes and anti-Stokes energy transfer mechanisms between two widely separated unequal quantum wells with a large energy mismatch ({Delta}) at low temperatures (T). Exciton transfer through dipolar coupling, photon-exchange coupling and over-barrier ionization of the excitons through exciton-exciton Auger processes are examined. The energy transfer rate is calculated as a function of T and the center-to-center distance d between the two wells. The rates depend sensitively on T for plane-wave excitons. For located excitons, the rates depend on T only through the T-dependence of the localization radius.
Date: December 6, 1999
Creator: LYO,SUNGKWUN K.
Partner: UNT Libraries Government Documents Department

Silicon Three-Dimensional Photonic Crystal and its Applications

Description: Photonic crystals are periodically engineered ''materials'' which are the photonic analogues of electronic crystals. Much like electronic crystal, photonic crystal materials can have a variety of crystal symmetries, such as simple-cubic, closed-packed, Wurtzite and diamond-like crystals. These structures were first proposed in late 1980's. However, due mainly to fabrication difficulties, working photonic crystals in the near-infrared and visible wavelengths are only just emerging. In this article, we review the construction of two- and three-dimensional photonic crystals of different symmetries at infrared and optical wavelengths using advanced semiconductor processing. We further demonstrate that this process lends itself to the creation of line defects (linear waveguides) and point defects (micro-cavities), which are the most basic building blocks for optical signal processing, filtering and routing.
Date: November 1, 2001
Creator: LIN, SHAWN-YU; FLEMING, JAMES G. & LYO, SUNGKWUN K.
Partner: UNT Libraries Government Documents Department

Magnetic Anticrossing of 1D Subbands in Coupled Ballistic Double Quantum Wires

Description: We study the low-temperature in-plane magnetoconductance of vertically coupled double quantum wires. Using a novel flip-chip technique, the wires are defined by two pairs of mutually aligned split gates on opposite sides of a s 1 micron thick AlGaAs/GaAs double quantum well heterostructure. We observe quantized conductance steps due to each quantum well and demonstrate independent control of each ID wire. A broad dip in the magnetoconductance at -6 T is observed when a magnetic field is applied perpendicular to both the current and growth directions. This conductance dip is observed only when 1D subbands are populated in both the top and bottom constrictions. This data is consistent with a counting model whereby the number of subbands crossing the Fermi level changes with field due to the formation of an anticrossing in each pair of 1D subbands.
Date: July 13, 2000
Creator: BLOUNT,MARK A.; MOON,JEONG-SUN; SIMMONS,JERRY A.; LYO,SUNGKWUN K.; WENDT,JOEL R. & RENO,JOHN L.
Partner: UNT Libraries Government Documents Department

Magnetoconductance of Independently Tunable Tunnel-Coupled Double Quantum Wires

Description: The authors report on their recent experimental studies of vertically-coupled quantum point contacts subject to in-plane magnetic fields. Using a novel flip-chip technique, mutually aligned split gates on both sides of a sub micron thick double quantum well heterostructure define a closely-coupled pair of ballistic one-dimensional (1D) constrictions. They observe quantized conductance steps due to each quantum well and demonstrate independent control of each ID constriction width. In addition, a novel magnetoconductance feature at {approximately}6 T is observed when a magnetic field is applied perpendicular to both the current and growth directions. This conductance dip is observed only when 1D subbands are populated in both the top and bottom constrictions. This data is consistent with a counting model whereby the number of subbands crossing the Fermi level changes with field due to the formation of an anticrossing in each pair of 1D subbands.
Date: July 13, 2000
Creator: BLOUNT,MARK A.; MOON,J.S.; SIMMONS,JERRY A.; LYO,SUNGKWUN K.; WENDT,JOEL R. & RENO,JOHN L.
Partner: UNT Libraries Government Documents Department

Photonic Band Gap Structures as a Gateway to Nano-Photonics

Description: This LDRD project explored the fundamental physics of a new class of photonic materials, photonic bandgap structures (PBG), and examine its unique properties for the design and implementation of photonic devices on a nano-meter length scale for the control and confinement of light. The low loss, highly reflective and quantum interference nature of a PBG material makes it one of the most promising candidates for realizing an extremely high-Q resonant cavity, >10,000, for optoelectronic applications and for the exploration of novel photonic physics, such as photonic localization, tunneling and modification of spontaneous emission rate. Moreover, the photonic bandgap concept affords us with a new opportunity to design and tailor photonic properties in very much the same way we manipulate, or bandgap engineer, electronic properties through modern epitaxy.
Date: August 1, 1999
Creator: FRITZ, IAN J.; GOURLEY, PAUL L.; HAMMONS, G.; HIETALA, VINCENT M.; JONES, ERIC D.; KLEM, JOHN F. et al.
Partner: UNT Libraries Government Documents Department

Final Report on LDRD Project: Development of Quantum Tunneling Transistors for Practical Circuit Applications

Description: The goal of this LDRD was to engineer further improvements in a novel electron tunneling device, the double electron layer tunneling transistor (DELTT). The DELTT is a three terminal quantum device, which does not require lateral depletion or lateral confinement, but rather is entirely planar in configuration. The DELTT's operation is based on 2D-2D tunneling between two parallel 2D electron layers in a semiconductor double quantum well heterostructure. The only critical dimensions reside in the growth direction, thus taking full advantage of the single atomic layer resolution of existing semiconductor growth techniques such as molecular beam epitaxy. Despite these advances, the original DELTT design suffered from a number of performance short comings that would need to be overcome for practical applications. These included (i)a peak voltage too low ({approx}20 mV) to interface with conventional electronics and to be robust against environmental noise, (ii) a low peak current density, (iii) a relatively weak dependence of the peak voltage on applied gate voltage, and (iv) an operating temperature that, while fairly high, remained below room temperature. In this LDRD we designed and demonstrated an advanced resonant tunneling transistor that incorporates structural elements both of the DELTT and of conventional double barrier resonant tunneling diodes (RTDs). Specifically, the device is similar to the DELTT in that it is based on 2D-2D tunneling and is controlled by a surface gate, yet is also similar to the RTD in that it has a double barrier structure and a third collector region. Indeed, the device may be thought of either as an RTD with a gate-controlled, fully 2D emitter, or alternatively, as a ''3-layer DELTT,'' the name we have chosen for the device. This new resonant tunneling transistor retains the original DELTT advantages of a planar geometry and sharp 2D-2D tunneling characteristics, yet also overcomes the ...
Date: July 1, 2002
Creator: SIMMONS, JERRY A.; MOON, JUENG-SUN; BLOUNT, MARK; LYO, SUNGKWUN K.; BACA, WES E.; RENO, JOHN L. et al.
Partner: UNT Libraries Government Documents Department