Physics Commons^™

Subthreshold Channel Leakage Current In Gaas Mesfet's, Wei Long

Theses

In this thesis, a physical model including the subthreshold conpensation properties is presented. The Poisson equation is solved analytically in one dimension for GaAs MESFET's with undoped substrates in the subthreshold region. The solution is then used to derive expressions for subthreshold drain current and subshreshold swing in MESFET's with undoped substrates. Very good agreement between experimental and analytical results is achieved.

Two key parameters (Nilo and Iso) that determine the subthreshold Characteristics have been analyzed as a function of residual acceptor concentration Na, deep level EL2 concentration Nt, channel doping concentration Nd and threshold voltage Vt. It is shown …

Measurement Of The Hall Coefficient And Electron Mobility Using Van Der Pauw Type Hall Effect Measurements, Hong-Sheng Luo

Theses

Hall effect measurement in the electrical characterization of semiconductor materials is very important. We set up the Hall effect measurement system and examined the system with a standard sample. The experimental results show that this Hall measurement system worked as well as expected. We also used this system to study the GaAs/GaAs and InGaAs/GaAs which grown by MBE. Finally, we disscussed and consided some common problems of Hall measurement. Some useful formulas and plots are presented.

Mbe Growth Of Inxga1-Xas/Gaas/Si Heterostructure System, Jun Liu

Theses

In this work, we grew the In_xGa_1-xAs/GaAs/Si (GaAs as buffer layer) by MBE technique. The surface of the buffer layer became microscopically rough as the thickness of the buffer layer increased and the growth mode of GaAs on Si underwent a change from three-dimensional to two-dimensional during the initial growth stage as indicated on the Reflection High Energy Electron Diffraction (RHEED) screen. The Scattering Electron Microscopy (SEM) observation of the etched surface of GaAs on Si showed that the structure of the buffer layer tended to be poly-crystalline and it was possible that a predominant orientation …

Nmr Computer Simulation Of Glassy And Powdered Samples : Application To Studies Of Sodium Borovanadate Glasses, Xian-Quan Zhang

Theses

A computer program is devised to simulate the nuclear magnetic resonance (NMR) spectra observed in powdered and glassy samples in the presence of both nuclear quadrupole and anisotropic chemical shift interactions. This method is performed for the central transition of NMR spectra of nuclei with half-integral spin I. Typical theoretical behavior of the powder pattern is discussed and the "noise" and "error" in the simulated spectra are analyzed. The computer simulation method is applied to the studies of 11B NMR spectra of the sodium borovanadate glass system for which a structural model is presented in the range for which glasses …

Low Temperature Performance Of Field Effect Transistors, Wei Zhu

Theses

The low temperature static characteristics of silicon junction field-effecttransistors (JFETs) have been investigated and analysed. The followingchanges were observed after cooling down the transistors: pinch-offvoltage and transconductance increases; and drain current is changedas a function of the drain-source voltage. It was found that there wasan increase in the amplifying properties and a reduction in noise voltageof cooled transistors. In addition, the temperature and voltage dependenceof leakage current have been studied. Temperatures below 77K are ofinterest in evaluating effects of impurity freezeout and temperatureabove 77K are important since actual device temperature will be aboutthe ambient. Operation of FET circuits at liquid …

Calibration Of Photoluminescence Experiment, Chihchuan Daniel Lee

Theses

Photoluminescence in a semiconductor at room temperature is quite difficult to distinguish from the many nonlasing optical lines from the laser, therefore, a blank test is very important. In so doing, the noises of the detector has to be taken into account. The calibration, however, mainly depends on the detector and is less dependent on other components. Instead of using black-body radiation light source and pyroelectric detector, we use globar lamp and PbS detector; because of the difficulty in the former case in doing alignment of optical path (invisible) and operating at a lower signal level from the detector. The …

Photoluminescence Study Of Gallium Arsenide, Aluminum Gallium Arsenide, And Gallium Antimonide Thin Films Grown By Metalorganic Chemical Vapor Deposition, John Mark Koons

Theses

The photoluminescence produced by four MOCVD grown epitaxial thin film samples was studied to give insight into sample quality. The four samples under this study were GaAs on a GaAs substrate, Al_.25Ga_.75As on a GaAs substrate, Al_.30Ga_.7OAs on a GaAs substrate, and GaSb on a GaSb substrate. Excitation was achieved through the use of the 514.0 nm line of an argon ion laser, and sample cooling was attained by use of a cryostat cooler using helium gas to attain a low temperature limit of 10°K. The GaAs and Al_.30Ga_{.7O …}

A Theoretical Study Of The Semiconductor Laser Structures With Lateral Discontinuity In The Optical Cavity, Yi Cai

Theses

A theoretical study of the semiconductor laser structures with lateral discontinuity in the optical resonant cavity is presented in this thesis. Specifically, the lateral discontinuity is referred to the lateral expansion structure newly invented for increasing the power output of semiconductor lasers while keeping single mode operation.

In the first part of the thesis (Chapter 2 and Chapter 3), an explicit expression for calculating the lateral discontinuity problems is formulated by the incorporation of mode-matching method. Our approach is based on the mode expansion theory developed for lossless micro-wave and optical fiber waveguides, but the effect of gain in active …

External Cavity Laser Power Stabilizer, Jie Ding

Theses

In this thesis, we want to design a stabilizer which does not depend on laser source--with external cavity.

In the first part of the thesis ( Chapter 2 and 3 ), we discuss the wave propagation in crystals and the modulation of optical radiation. From the main two types electro-optic modulations, Phase Modulation and Transverse Modulation, we know that the transverse modulation shows an increase in the frequency limit or useful crystal length of (1-c0/ncm)^-1, and we will use this type modulation in this thesis.

The second part of the thesis is the procedure of design and experiment. …

A Thermoelastic Model Applied To Stress Control In Laser Heating Of Ceramics, Jeff Alexander Wagner

Theses

Localized laser heating is widely used in materials processing. In extending these techniques to materials with relatively low thermal conductivities and ductilities such as ceramics and glasses, existing methods must be modified to control the high thermal stresses which are associated with the localized heating of these materials. Thermal profiles must be designed to minimize damage to regions adjacent to the processed area. To achieve this with single beam sources the power and radius can be varied in time, or the beam can be moved across the surface in a programmed pattern to achieve the desired thermal profile.

In this …