Thesis (Ph. D.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 107-109).

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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2002. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.

Thesis (Ph. D.)--University of Washington, 1995. / Vita. Includes bibliographical references (leaves [168]-171).

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

The Hall coefficient and conductivity of silicon films vacuum deposited on 0° and 60° sapphire at 850°C to 1050°C were measured from 100°K to 550°K. Films made from 0.094 Ω-cm p type and 1 Ω-cm n type silicon sources were prepared by electron bombardment heating of the source in a vacuum of 5 x 10⁻⁷ to 10⁻⁶ torr. The orientation and crystallinity of the films were investigated using electron diffraction. It was found that defects in the films introduced both donor and acceptor levels. The heavy compensation thus produced in films deposited at lower temperatures lead to a very low hole concentration. All films were p type at room temperature showing that the acceptor levels slightly dominated the donor levels. The films deposited on 0° sapphire indicated fewer defects than those deposited on 60° sapphire. At high temperature (> 950°C) doping of the silicon by aluminum atoms from the substrate was appreciable. The Hall mobility of the films made from the p type source material decreased with increasing temperature of deposition. This apparent anomaly is explained by the use of the polycrystalline film model suggested by Volger (1950). / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The technique of ellipsometry was applied to the study of nonuniform anodic oxide films resulting from electrolyte incorporation into the oxide on growth. Ellipsometry results obtained in air and in situ on oxides formed on Ta in phosphoric acid are consistent with the results of tracer studies in which the oxide consists of two layers which grow simultaneously due to metal and oxygen ion transport during anodization, and further that electrolyte incorporation into the outer layer on growth modifies its properties with respect to the inner layer. The ellipsometry results were not consistent with a single homogeneous layer film or with a film possessing an index of refraction changing linearly with thickness. Thus ellipsometry provides a new, nondestructive method of determining ion transport numbers. The index of refraction and thickness of each layer were obtained by curve fitting ellipsometry results obtained as a function of increasing oxide thickness. Computer methods for solving the ellipsometry equation and curve fitting are given. Computed results are given and discussed for cases of one and two layer films growing on a metal. Finally, an error analysis of ellipsometry is made. Ellipsometry results were obtained and curve-fitted for oxides grown in various solutions, at different rates and for anodization in a sequence of electrolytes. The major findings of this part of the study are as follows: Electrolyte incorporation decreases ionic conductivity, dielectric constant and index of refraction. At constant current formation, the fraction of oxide made up by the outer layer increases with current density, and electrolyte concentration, and depends on previous formation of the oxide. The log J-E characteristics at constant voltage in dilute phosphoric acid are curved and occur at higher fields than those for dilute sulphuric acid. Analysis of the above results indicates that: a) the conduction process is bulk controlled b) ionic conduction and dielectric properties arise from the same process and c) that electrolyte incorporation is responsible for part if not all the curvature in the logJ-E characteristics of ionic conduction. Photo-stimulated growth at low electric fields was investigated by ellipsometry. The effect of radiation is to first modify the properties of the existing oxide after which photo-stimulated growth occurs accompanied by a build up of secondary current. The secondary photocurrent is ionic in nature and the radiation rather than the applied field is responsible for the generation of ions to sustain this current. The photo-grown oxide consists of two layer with the outer layer having a much lower index of refraction than normally grown oxide. The thermal recrystallization of stripped anodic oxide films was studied using transmission electron microscopy. Various diffraction patterns were obtained and analyzed. The major result in terms of ionic conduction is that electrolyte incorporation inhibits recrystallization, again, consistent with a decreased ionic mobility with incroporation. A critical test has been devised and applied to a recently proposed theory of ionic conduction, the dielectric polarization theory. This theory postulates that the autocatalytic build up of ionic current on applying a constant high field to the oxide is due to an internal field controlled process and that the rate of build up of polarization (P) towards its equilibrium value (P₀) is enhanced by the passage of current, J, given by dp/dt = AJ(P₀-P). It is shown that this theory predicts an increase in small signal capacitance during the passage of the transient. However, measurements indicate that the capacitance decreases. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The dielectric polarization processes, conduction mechanisms and space charge effects occurring in tantalum / tantalum pentoxide / metal devices are investigated. The dielectric properties are analyzed on the basis of an ionic relaxation process with a nearly flat distribution of activation energies. This distribution leads to step response polarization currents following an inverse time law. The effect of an injected electronic space charge on the response of the device due to the removal of a step voltage is analyzed and results are given demonstrating this effect. The devices used exhibit a rectification behaviour. For tantalum positive the currents follow a Schottky law and for tantalum negative, the bulk Poole-Frenkel law. Hysteresis effects are observed as well as the effects of a space charge on the Schottky law currents. On one sample, sufficiently high fields causes an increase in the conductance by a factor of 10³ to 10⁵. For this deformed sample, no hysteresis or rectification is observed and the currents follow a Schottky law for both polarities. The validity of the ionic relaxation model is discussed in light of the observed dielectric losses at low temperatures. The experimental results indicate that an electronic rather than an ionic process could be responsible for the dielectric losses. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate