Physical Sciences and Mathematics Commons^™

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 …

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. …

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 …

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 …

Far Infrared Fourier Transform Spectroscopy Using Ring Interferometer, Changqing Qiu

Theses

A circular mirror interferometer named ring interferometer, which was designed by Dr. K.D. Moller, was built and set up for far-infrared Fourier transform spectroscopy. The ring interferometer has ten circular mirrors with the same area. By applying Fraunhofer diffraction theory, the calculation shows that the ring interferometer will have large diffraction angle range compared with lamellar grating interferometer which has rectangular mirrors with same width. Therefore the ring interferometer will be more efficient than lamellar grating in far-infrared spectroscopy. The experimental results show that this ring interferometer will work as expected.

In addition, a "home made" helium cooled detector was …

Non-Contact Measurement For Thermal Conductivity Of Diamond-Like And Hard Carbon Thin Films, Ganming Qin

Theses

In this research work, non-contact temperature measurement was applied to determine the thermal conductivity of diamond-like and hard carbon thin films. Dielectric materials widely used as thin films in device manufacturing are SiO₂, Si₃N₄, polymer, and etc. However, their heat dissipating capacity is not good for power devices. It is necessary to develop a new material for this purpose. Diamond crystal is a high quality dielectric material. It has the highest room-temperature thermal conductivity [k=20W (cm · K) at 20°C] among all materials. In addition, it has high electrical resistivity ( >10¹⁶ Ω …

A Theoretical Model For Biased Superlattice Devices, Michael Ferner

Theses

A model describing the subband structures and tunneling characteristics of superlattices is presented. The model solves the envelope function equations by the transfer matrix technique. The results are codified in a Fortran program, and the model is applied to several structures.

Superlattice have been studied extensively, however many new structures await investigation.

This model is presented as a preliminary design tool. The program allows a designer to do preliminary calculations. This type of investigation guides a designer toward a goal by making possible a large number of calculations on many different structures.

Instrumentation For The Characterization Of 10 Micron Focal Plane Array Detectors, Zhen Zong

Theses

In the atmospheric window thermal imaging technology, the 8-12 micron spectral range is of particular interest, since the 300 K black body radiation peaks at around 10 micron with a flux as large as 1019photons/cm2sec. Due to its extreme temperature sensitivity for the 300 K background imaging, this long wave length infrared atmospheric window is vital for a variety of applications. A monolithic GaAs multiple quantum well (MQW) IR image sensor in this spectrum region is being developed in the research group of Profs. K. Chin and J. C. Hensel.

The work performed here is to set up a computer-controlled …

Quantitative Measurement Of Pyrolysis And Combustion Species Concentration By Molecular-Beam-Sampling-Mass-Spectrometry, Xian Zhong

Theses

A molecular-beam-sampling apparatus utilizing both a time-of-flight mass spectrometer with vacuum ultraviolet (VUV) photoionization and a quadrupole mass spectrometer with electron impact ionization is described. These systems are used to analyze reactants and products, as well as reactive intermediates, from flow tube experiments at reduced pressures and elevated temperatures. It is shown that the quadrupole signal sensitivity can be predicted using literature cross sections which are based upon the atom hybridization within the various molecules. Measurements of the VUV photoionization sensitivity for stable species led to development of a group additivity approach to predict cross sections. This approach was extended …

A Theoretical Study Of The Subband Structures And Tunneling In Polytype Heterostructures, Hong Chen

Theses

A theoretical study of the electronic and optical properties in polytype heterostructures is presented in this thesis.

In the first part of the thesis (Chap. 2 and Chap. 3), an explicit expression for calculating the subband structure and tunneling is formulated by the incorporation of the envelope function approximations and the transfer matrix technique. It is based on the k*p theory as done to date, but contains two significant improvements: a more realistic treatment of the spatial and energetic dependance of effective masses and band edges; the availability of the calculations, in favor of direct numerical evaluation, to various quantum …