Full Hydrodynamic Simulation of GaAs MESFETs

A finite difference upwind discretization scheme in two dimensions is presented in detail for the transient simulation of the highly coupled non-linear partial differential equations of the full hydrodynamic model, providing thereby a practical engineering tool for improved charge carrier transport simulations at high electric fields and frequencies. The discretization scheme preserves the conservation and transportive properties of the equations. The hydrodynamic model is able to describe inertia effects which play an increasing role in different fields of micro- and optoelectronics, where simplified charge transport models like the drift-diffusion model and the energy balance model are no longer applicable. Results of extensive numerical simulations are shown for a two-dimensional MESFET device. A comparison of the hydrodynamic model to the commonly used energy balance model is given and the accuracy of the results is discussed.Comment: 18 pages, LATE

Ultrafast-ultrafine probing of high-speed electrical waveforms using a scanning force microscope with photoconductive gating

Picosecond photoconductivity in low-temperature-grown GaAs (LT GaAs) has been used to provide temporal resolution both in rigid probes and in scanning force microscope probes. This article reviews the fabrication and use of such probes. 2.5 ps temporal resolution and few microvolts sensitivity are obtained at arbitrary points on circuits with a spatial definition of 100 nm. Rigid probes are tested in application to analogue and digital circuits. As an alternative to electron beam testing, scanning force probes are applied to in situ imaging and waveform measurement. Finally, the use of time-resolved waveform analysis with scanning-force microscopy probes with semiconductor laser sources is demonstrated.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43337/1/11082_2004_Article_BF00820152.pd

GaAs optoelectronic logic devices.

She Tsz Chung William.Thesis (M.Phil.)--Chinese University of Hong Kong, 1994.Includes bibliographical references (leaves 127-133).Chapter 1. --- IntroductionChapter 2. --- Review of Optical Logic --- p.11-28Chapter 2.1 --- All-Optical ApproachChapter 2.2 --- Optoelectronic ApproachChapter 2.3 --- Comparison of the Two ApproachesChapter 3. --- High Speed Photodetectors applied in Optoelectronic Logic Design --- p.29-40Chapter 3.1 --- Photoconductive SwitchChapter 3.2 --- Metal-Semiconductor-Metal PhotodetectorChapter 3.3 --- Design of Simple Logic GatesChapter 4. --- Device Fabrication and Characterization --- p.41-59Chapter 4.1 --- Design of Basic StructureChapter 4.2 --- FabricationChapter 4.3 --- Mounting of DeviceChapter 4.4 --- CharacterizationChapter 5. --- Experimental Technique --- p.60-74Chapter 5.1 --- Measurement ProcedureChapter 5.2 --- Optical SourcesChapter 5.3 --- Optical AlignmentChapter 5.4 --- Control of Optical Path DelayChapter 5.5 --- Measurement AutomationChapter 6. --- Demonstration of Optoelectronic Logic Devices --- p.75-110Chapter 6.1 --- OR GateChapter 6.2 --- Exclusive-OR GateChapter 6.3 --- Exclusive-NOR GateChapter 6.4 2 --- to 4 DecoderChapter 7. --- Discussion --- p.111-124Chapter 7.1 --- ImprovementsChapter 7.2 --- Extensions of this ProjectChapter 7.3 --- Prospects and Limitations of this ApproachChapter 8. --- Conclusion --- p.125-126References --- p.127-133AppendixChapter I. --- List of Instruments --- p.134-136Chapter II. --- Properties of GaAs --- p.137Chapter III. --- List of Accepted and Submitted Publications during the Period of Study --- p.13

Hardware Development of an Ultra-Wideband System for High Precision Localization Applications

A precise localization system in an indoor environment has been developed. The developed system is based on transmitting and receiving picosecond pulses and carrying out a complete narrow-pulse, signal detection and processing scheme in the time domain. The challenges in developing such a system include: generating ultra wideband (UWB) pulses, pulse dispersion due to antennas, modeling of complex propagation channels with severe multipath effects, need for extremely high sampling rates for digital processing, synchronization between the tag and receivers’ clocks, clock jitter, local oscillator (LO) phase noise, frequency offset between tag and receivers’ LOs, and antenna phase center variation. For such a high precision system with mm or even sub-mm accuracy, all these effects should be accounted for and minimized. In this work, we have successfully addressed many of the above challenges and developed a stand-alone system for positioning both static and dynamic targets with approximately 2 mm and 6 mm of 3-D accuracy, respectively. The results have exceeded the state of the art for any commercially available UWB positioning system and are considered a great milestone in developing such technology. My contributions include the development of a picosecond pulse generator, an extremely wideband omni-directional antenna, a highly directive UWB receiving antenna with low phase center variation, an extremely high data rate sampler, and establishment of a non-synchronized UWB system architecture. The developed low cost sampler, for example, can be easily utilized to sample narrow pulses with up to 1000 GS/s while the developed antennas can cover over 6 GHz bandwidth with minimal pulse distortion. The stand-alone prototype system is based on tracking a target using 4-6 base stations and utilizing a triangulation scheme to find its location in space. Advanced signal processing algorithms based on first peak and leading edge detection have been developed and extensively evaluated to achieve high accuracy 3-D localization. 1D, 2D and 3D experiments have been carried out and validated using an optical reference system which provides better than 0.3 mm 3-D accuracy. Such a high accuracy wireless localization system should have a great impact on the operating room of the future

Frequency and Time Domain Measurements of Optical Fibre Response.

This thesis examines a new technique for measuring the transfer function of optical fibre waveguide directly in the frequency domain with special emphasis on the phase response. A detailed theory of the feasibility and limitation of this technique is presented, and its optimisation for optical fibre measurement is discussed. A complete measurement system has been built and set to perform the measurement automatically under computer control. This system performs both frequency and time domain measurements to determine the transfer function and impulse response of optical fibre. The transfer function and impulse response of a 100m step-index fibre have been measured using a HeNe laser source (wavelength of 0.6328mum) upto a frequency of 550MHz, and those of a 900m graded-index fibre up to a frequency of 1275MHz using a cw laser diode (wavelength of 0.87mum), using both techniques. The contribution of different sources of error in both measurement methods is also examined. Finally the relative advantages as well as disadvantages of the two measurement techniques are discussed

Spaceborne sensors (1983-2000 AD): A forecast of technology

A technical review and forecast of space technology as it applies to spaceborne sensors for future NASA missions is presented. A format for categorization of sensor systems covering the entire electromagnetic spectrum, including particles and fields is developed. Major generic sensor systems are related to their subsystems, components, and to basic research and development. General supporting technologies such as cryogenics, optical design, and data processing electronics are addressed where appropriate. The dependence of many classes of instruments on common components, basic R&D and support technologies is also illustrated. A forecast of important system designs and instrument and component performance parameters is provided for the 1983-2000 AD time frame. Some insight into the scientific and applications capabilities and goals of the sensor systems is also given

Photodetectors

In this book some recent advances in development of photodetectors and photodetection systems for specific applications are included. In the first section of the book nine different types of photodetectors and their characteristics are presented. Next, some theoretical aspects and simulations are discussed. The last eight chapters are devoted to the development of photodetection systems for imaging, particle size analysis, transfers of time, measurement of vibrations, magnetic field, polarization of light, and particle energy. The book is addressed to students, engineers, and researchers working in the field of photonics and advanced technologies

NASA SBIR abstracts of 1991 phase 1 projects

The objectives of 301 projects placed under contract by the Small Business Innovation Research (SBIR) program of the National Aeronautics and Space Administration (NASA) are described. These projects were selected competitively from among proposals submitted to NASA in response to the 1991 SBIR Program Solicitation. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 301, in order of its appearance in the body of the report. Appendixes to provide additional information about the SBIR program and permit cross-reference of the 1991 Phase 1 projects by company name, location by state, principal investigator, NASA Field Center responsible for management of each project, and NASA contract number are included

Terahertz Technology and Its Applications

The Terahertz frequency range (0.1 – 10)THz has demonstrated to provide many opportunities in prominent research fields such as high-speed communications, biomedicine, sensing, and imaging. This spectral range, lying between electronics and photonics, has been historically known as “terahertz gap” because of the lack of experimental as well as fabrication technologies. However, many efforts are now being carried out worldwide in order improve technology working at this frequency range. This book represents a mechanism to highlight some of the work being done within this range of the electromagnetic spectrum. The topics covered include non-destructive testing, teraherz imaging and sensing, among others

Picosecond photophysical processes in iodoanthracenes

Picosecond photophysical processes in 2- and 9-iodoanthracene in cyclohexane at room temperature were studied by triplet-triplet transient absorption spectroscopy between 420-500 nanometers. For small amounts of excess vibronic energy in S(,1), intersystem crossing from the first excited singlet state into high triplet states T(,n) (n \u3e 1) with subsequent internal conversion to T(,1) or dissociation from the upper triplet manifold is suggested as a primary pathway for nonradiative relaxation. Rate constants for the processes were estimated using the results from previous fluorescence studies and the population risetime data for T(,1). Analyses of the photoproducts generated by excitation at two different wavelengths into the first excited singlet state reveal a vibronic level dependence of the photodissociation yield, indicating that photodissociation can proceed via at least two different mechanisms in the iodoanthracenes;Stimulated Raman processes and self-action effects are shownto be primarily responsible for the generation of a picosecondcontinuum when 532 nm picosecond pulses are focused into aCCl(,4) continuum cell. An experimental assessment of the artifactsintroduced by the angular distribution of continuum light on the;triplet-triplet absorption spectra of acridine is given and proceduresto minimize these effects are suggested; (\u271)DOE Report IS-T-1042. This work was performed under contract number W-7405-Eng-82 with the U.S. Department of Energy