Thesis (Ph. D.)--University of Chicago, 1920. / "Private edition, distributed by the University of Chicago libraries, Chicago, Illinois." "Reprinted from the Physical review, n.s., vol. XVII, no. 3, March, 1921." Also available on the Internet.

Thesis (M.S.) OGI School of Science & Engineering at OHSU, September 2007. / Includes bibliographical references (leaves 72-74).

Thesis (M.S.)--Oregon Graduate Center, 1985.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (site viewed May 16, 2007). PDF text: xiv, 146 p. : ill. (some col.) ; 8.10Mb. UMI publication number: AAT 3237057. Includes bibliographical references. Also available in microfilm and microfiche formats.

Th.--Sci. phys.--Toulouse 3, 1978. N°: 845.

Th.--Sci. phys.--Toulouse 3, 1978. N°: 839. / Rés. en fr. et angl.

The present work was initially aimed at providing an explanation for some of the phenomena that occur in the ionosphere at sunrise. The approach that was taken was to determine the changes that take place on a theoretical model of the ionosphere and then to compare these with observations. A prerequisite for this approach was a theoretical model that would show, among other things, a bifurcation of the F layer during daytime without making unjustified arbitrary assumptions. The absence of such a model, particularly as far as non-equilibrium conditions are concerned, resulted in the present attempt to provide such a model for the F1 region.

The purpose of this thesis is to investigate the operation of GaAs field-effect transistors with particular attention to the existence of negative resistance regions in the current-voltage characteristics, velocity overshoot effects, the role of substrate, and the role of heterojunctions. The approach used is to solve the electron transport equation using the Monte Carlo method which accounts for non-local effects in electron transport. Arguments are presented to support the contention that the negative resistance regions in the current-voltage characteristics observed in some experimental devices and produced by other researchers' computer simulations are attributed, in part, to the negative differential mobility of GaAs. The main reason of the existence of this negative resistance is related to the active layer thickness and it will be explained in terms of the rotation of the velocity vector. Electron velocity overshoot, a consequence of non-local effects, is examined in terms of gate length. The velocity overshoot becomes significant for FET structures with gates less than a micron in length and has many significant effects on the device performance. It is found also that velocity overshoot accounts for the undesirable saturation characteristics of submicron gate length GaAs FET which are observed in practical devices. However, it was also found that the presence of a low-doped n-type GaAs substrate below the active layer removes the negative resistance regions in the current-voltage characteristics. This is attributed to the effect of carrier injection from the active layer into the substrate which leads to the decrease of the effective channel thickness. This then will decrease the transconductance of the device, increase the gate pinchoff voltage and lower the device frequency response. This degradation of device's performance depends entirely on the purity and properties of the substrate. The performance of substrated FETs can be improved by preventing electron penetration into the substrate. This situation can be reached by using AlGaAs substrate whose energy band gap is higher than that of GaAs which then leads to electron confinement in the active layer. The use of AlGaAs in FETs can be in different forms. These will also be demonstrated in this thesis.

Hall effect and resistivity measurements have been carried out as a function of hydrostatic pressure and temperature on a number of samples of indium phosphide ranging from exceptionally pure to highly doped. In the case of pure and lightly doped InP an iterative solution of the Boltzmann Equation has been used successfully to describe the temperature and pressure dependence of mobility over the helium temperature range. Measurements on the highest mobility samples of InP ever grown suggest that the conduction band deformation potential is 6. 7eV. For the case of highly doped material it was found that a theory of scattering from a correlated distribution of impurities describes both the temperature and pressure dependence of mobility well. Pressure dependent mobility measurements on a sample having an impurity density close to the Mott transition suggest that the inclusion of impurity band conduction in the analysis is necessary even at nitrogen temperatures and above. Such an analysis is used successfully to describe the temperature and pressure dependence of both mobility and Hall carrier concentration.

Separation of rare or expensive isotopes, whether radioactive or stable, requires a high efficiency of the separation process. Electromagnetic isotope separation is the most widely-used of all separation processes. Its separation efficiency depends mainly upon the ionization efficiency of its ion source. An Electron Cyclotron Resonance (ECR) ion source has been developed for the separation of both stable and radioactive isotopes on account of its high ionization efficiencies. The maximum ionization efficiencies achieved with the ECR ion source for singly charged ions for a range of materials were: radioiodine (8%), carbon (10%), nitrogen (26%), oxygen (53%), neon (31%) and xenon (83%). A computer code ECREFF, based on the atomic processes which occur in the plasma, is described for the calculation of the ionization efficiency of an ECR ion source. The experimental and calculated data are compared.