The mainly research is by adding the rare-earth metal gadolinium salts with sol-gel process to form the gadolinium -doped titanium dioxide, and by forming the liquid crystal template with the non-ionic surfactant to form the mesostructure of titanium dioxide. And the research has aimed at the using different non-ionic surfactant, the different pH value, the different solvent of water/ethanol ratio, the hydrothermal process or not, and the gadolinium content. We discussed these factors how to affect the titanium dioxide in the physical property, the chemical property, or structure influence. Using the XRD to measure the mesostucture of titanium dioxide and the crystallization of titanium dioxide, and we observe the shape and particle size of titanium dioxide with SEM. We use UV-visible spectrum to observe absorption spectrum of titanium dioxide. The result discovers that surfactant effect is using triblock copolymer, poly (ethylene oxide) - poly (propylene oxide) - poly (ethylene oxide), the titanium dioxide has anatase and rutile crystallization, and particle aggregation. The pH affects the partic le size and the shape. In pH is 5.8, the titanium dioxide has anatase and rutile crystallization. In water/ethanol ratio effect, we use solvent including ethanol, the titanium dioxide has anatase and rutile. Through hydrothermal process, titanium dioxide has little brookite crystallization and the few fibrous titanium dioxides. The doping gadolinium effect is the anatase is reducing with gadolinium content increasing, and from the UV-visible spectrum, the doping gadolinium titanium dioxide has the red shift. The titanium dioxide using polyoxyethylene sorbitan monostearate and doping gadolinium has the anatase, and absorbs a longer wavelength, and when the doping content is 1% titanium dioxide has a better absorption.

Thesis (Ph. D.)--University of Washington, 2007. / Includes bibliographical references (leaves 181-186).

Indium nitride (InN) is a group III-V semiconductor that is part of the Al,Ga:N family. It is an infrared bandgap semiconductor with great potential for use in photovoltaic applications. Being an intrinsically n-type material, p-type doping is naturally one of the ongoing hot topics in InN research, which is of interest in the fabrication of pn junctions. Plasma-assisted molecular beam epitaxy (PAMBE) grown Mg doped InN thin film was investigated via systematic optical characterizations. Photoluminescence (PL) measurement has been a key part of the research, exhibiting a wide range of spectral lines between 0.54 and 0.67 eV. In a critical Mg concentration range of 2.6×10¹⁷ and 1.0×10¹⁸ cm⁻³, a strong luminescence line at 0.6 eV has been associated with a Mg-related deep acceptor. Correspondingly, a variable magnetic field Hall (VFH) effect measurement has successfully probed a buried hole-mediated conductivity path underneath a surface electron accumulation layer. This specific doping range also led to a manifestation of a “true” band-to-band transition at 0.67 eV. Such an observation has not previously been reported for InN and in our case this assignment is convincingly supported by the quadratic characteristic of the excitation power law. This established that a rigorous control of Mg flux can sufficiently compensate the background electron concentration of InN via the substitutional incorporation on In sites (Mg_In). However, introduction of donor-like complexes somewhat suppressed this process if too much Mg or even alternative dopants such as Zn and Mn were used. Also distinctively observed was a strongly quenched PL quantum efficiency from heavily doped films, where time-resolved differential transmission (TRDT) measurement showed a biexponential carrier lifetime decay curve owing to the onset of Auger recombination processes. These observations certainly have profound implications for devices and beyond.

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No description available.

The optical properties of Mg-doped InN thin films grown on YSZ substrates have been investigated by photoluminescence (PL). A series of InN:Mg samples with various Mg cell temperatures (TMg) were produced by molecular beam epitaxy. The effect of Mg concentration on PL emission properties have been explored by various excitation power and temperature dependent measurements. The PL spectra as a function of excitation power exhibited a pronounce blueshift, indicating prominent band filling caused by the Burstein-Moss effect. Meanwhile, a typical redshift was observed as temperature increased due to bandgap shrinkage. The samples with TMg below 210 ˚C have a dominant peak at energy of 0.68 eV. In contrast, the PL peak emissions for films with a high TMg between 210~230 ˚C were centred near 0.6 eV. No PL emission was observed from the films with TMg above 230 ˚C. By fitting with an empirical Arrhenius equation, the activation energies yield approximately 20 meV and 15 meV for the lower and higher energy transitions, respectively. The fundamental optical properties of Zn doped InN were also examined. InN:Zn films were grown under In-rich conditions. The samples showed well defined PL emission spectra implying that the quality of the film has been improved over the Mg-doped series. The PL spectra of InN:Zn exhibited prominent features containing various emission peaks. The combination of excitation power and temperature dependent measurements supports a precise determination for the origins of the observed transitions. The comparison between the optical properties of Mg and Zn doped InN provide the motivation for more precise quantitative interpretation of p-type InN.

Thesis (Ph.D.) -- McMaster University, 1997. / Includes bibliographical references Also available via World Wide Web.

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No description available.

Complementary delta-doped AlGaAs/GaAs Heterojunction Field Effect Transistor (CHFET) devices and circuits were fabricated using MBE and a 2�� non-planar gate recess process. Several schemes were used in an attempt to improve the performance of the p-channel HFETs. These included delta-doping, carbon-doping and dipole-doping. Circuits and individual n- and p- channel devices were fabricated on a stacked delta-doped complementary structure. The circuits failed to perform due to complications with adjusting the threshold voltage. However, Individual devices were successfully characterized, p-channel devices with extrinsic transconductances up to 14 mS/mm, n-channel devices with extrinsic transconductances up to 120 mS/mm and a unity power gain bandwidth of 5.5 GHz. / Graduation date: 1995