The design, simulation, and initial fabrication of a novel ultra-compact 2x2 silicon multimode-interference device evanescently coupled to a dual germanium metal-semiconductor-metal (MSM) photodetector is presented. For operation at the standard telecom wavelength of 1.5 µm, the simulations demonstrate high-speed operation at 30 GHz, low dark current in the nanoamp range, and external quantum efficiency of 80%. Error analysis was performed for possible tilt error introduced by hybrid integration of the MSM layer on top of the MMI waveguides by use of surface mount technology (SMT) and direct wafer bonding.

The low thermal conductivity of gallium arsenide compared to silicon results in self-heating effects in GaAs MESFETs that limit the electrical performance of such devices for high power applications. To date, analytical thermal models of self heating in GaAs MESFETs are based on the assumption of a uniformly heated channel. This thesis presents a two dimensional analysis of the electrothermal effect of this device based on the two dimensional power density distribution in the channel under various bias conditions. The numerical simulation is performed using the finite difference technique. The results of the simulation of an isothermal MESFET without heat effects is compared with various one dimensional analytical models in the literature. Electro thermal effects into the two-dimensional isothermal MESFET model allowed close examination of the temperature profile within the MESFET. The large gradient in power distribution results in a localized heat source within the channel which increases the overall channel temperature, which shows that the assumption of a uniformly heated channel is erroneous, and may lead to an underestimation of the maximum channel temperature. / Graduation date: 1992

Graduation date: 1992

High speed photodetectors are a necessary element in broad band digital and analog optical communication systems. In this thesis easily integrable planar high speed photodetectors made on undoped semi-insulating (SI) GaAs substrates are modeled and tested. The fabrication process of the detectors is fully compatible with GaAs metal-semiconductor field effect transistor (MESFET) processing technology. Interdigitated fingers are used as the contacts to achieve both high sensitivity and large bandwidth. Detectors made with both ohmic and Schottky contacts are fabricated and tested. The equivalent circuit elements of the interdigitated structure are modeled using accurate lumped element circuit models associated with the various discontinuities of the structure. The results of the model agree well with the experimental results as well as with other published results. Numerical simulation of the SI-GaAs metal-semiconductor- metal (MSM) photodetector is performed. The carriers are tracked after an ideal optical pulse is applied and the intrinsic current as a function of time is computed. Then the influence of all the external circuit elements is included and the output current across the load resistor is computed. The simulated response is compared with other published models. The electrical and optical characteristics of the detectors are measured. For ohmic contact detectors, the dark current increases linearly with bias until some critical field is reached beyond which the dark current increases nonlinearly with bias. The time response of the detectors is measured with a 10 ps pulsed laser operating at - 600 nm and also with a pulsed GaAs /AlGaAs semiconductor laser operating at 850 nm. The ohmic and Schottky contact detectors have approximately the same rise time. The fall time of the Schottky contact detector is much smaller than the fall time of ohmic contact detector. The long fall time of the ohmic detector does not depend on the spacing between contacts. This long fall time is due to the large barrier that exists near the ohmic metal/SI-GaAs cathode contact. No such barrier exists for SI-GaAs MSM photodetector. The simulated impulse response of the SI-GaAs MSM photodetector is compared with the measured impulse response. / Graduation date: 1991

Electronic devices, for logical and memory applications, are constructed based on bistable electronic units that can store binary information. Molecular electronics proposes the use of single molecules—with two distinctive states of conductance—as bistable units that can be used to create more complex electronic devices. The conductance of a molecule is strongly influenced by the contacts used to address it. The purpose of this work is to determine the electrical characteristics of several candidate molecular junctions, which are composed of a molecule and contacts. Specifically, we are interested in determining whether binary information, “0” or “1,” can be encoded in the low- and high-conductance states of the molecular junctions. First, we calculate quantum-mechanically the electronic structure of the molecular junction. Second, the continuous electronic states of the contacts, originated from their infinite nature, are obtained by solving the Schrödinger equation with periodic boundary conditions. Last, the electron transport through the molecular junctions is calculated based on a chemical interpretation of the Landauer formalism for coherent transport, which involves the information obtained from the molecule and the contacts. Metal-molecule-metal and metal-molecule-semiconductor junctions are considered. The molecule used is an olygo(phenylene ethynylene) composed of three benzene rings and a nitro group in the middle ring; this molecule is referred hereafter as the nitroOPE molecule. Gold, silicon, and metallic carbon nanotubes are used as contacts to the molecule. Results from the calculations show that the molecular junctions have distinctive states of conductance for different conformational and charge states. High conductance is found in the conformation in which all the benzene rings of the nitroOPE are coplanar. If the middle benzene ring is made perpendicular to the others, low conductance is found. Also, the negatively charged junctions (anion, dianion) show low conductance. Whenever a semiconducting contact is used, a flat region of zero current is found at low bias voltages. The results indicate that the use of Si contacts is possible; however, because of the flat region, the operating point of the devices needs to be moved to higher voltages.

No description available.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23901号 / 工博第4988号 / 新制||工||1779(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 田中 功, 教授 杉村 博之, 准教授 野瀬 嘉太郎 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Bibliography: p. 269-276. / xxx, 306 p. : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The main objective of this thesis is to create a significant advance in the area of solid-state imaging via the research of an image sensor that can be ultimately integrated with high-speed gallium arsenide (GaAs) processing circuitry on a common substrate chip. / Thesis (Ph.D.)--University of Adelaide, Dept. of Electrical and Electronic Engineering, 1997

Thesis (M.S.)--Florida State University, 2005. / Advisor: Mark H. Weatherspoon, Florida State University, College of Engineering, Dept. of Electrical and Computer Engineering. Title and description from dissertation home page (viewed Jan. 26, 2006). Document formatted into pages; contains x, 107 pages. Includes bibliographical references.

This work presents the bottom-up fabrication of DNA origami-assembled metal nanowires and metal-semiconductor junctions, and their electrical characterization. Integration of metal and semiconductor nanomaterials into prescribed sites on self-assembled DNA origami has facilitated the fabrication of electronic nanomaterials, whereas use of conventional tools in their characterization combines bottom-up and top-down technologies. To expand the contemporary DNA-based nanofabrication into nanoelectronics, I performed site-specific metallization of DNA origami to create arbitrarily arranged gold nanostructures. I reported improved yields and conductivity measurements for Au nanowires created on DNA origami tile substrates. I measured the conductivity of C-shaped Au nanowires created on DNA tiles (∼130 nm long, 10 nm diameter, and 40 nm spacing between measurement points) with a four-point measurement technique which revealed the resistivity of the gold nanowires was as low as 4.24 × 10-5 Ω m. Next, I fabricated DNA origami-templated metal-semiconductor junctions and performed electrical characterization. Au and Te nanorods were attached to DNA origami in an alternating fashion. Electroless gold plating was used to create nanoscale metal--semiconductor interfaces by filling the gaps between Au and Te nanorods. Two-point electrical characterization indicated that the Au--Te--Au junctions were electrically connected, with non-linear current--voltage curves. Finally, I formed metal-semiconductor nanowires on DNA origami by annealing polymer-encased nanorods. Polymer-coated Au and Te nanorods pre-attached to ribbon-shaped DNA origami were annealed at 170°C for 2 min. Gold migration occurred onto Te nanorods during annealing and established electrically continuous interfaces to give Au/Te nanowires. Electrical characterization of these Au/Te/Au assemblies revealed both nonlinear current-voltage curves and linear plots that are explained. The creation of electronic nanomaterials such as metal nanowires and metal-semiconductor junctions on DNA origami with multiple techniques advances DNA nanofabrication as a promising path toward future bottom-up fabrication of nanoelectronics.