A series of as-grown ZnO layers have been electrically characterised by the temperature dependent (20 – 300 K) Hall-effect technique. The ZnO layers were grown by metal organic chemical vapour deposition (MOCVD) on glass substrates under various growth conditions. The temperature dependent Hall-effect technique produced mobility and carrier concentration measurements. These measurements were found to be reproducible and reliable. The carrier concentration data for the layers was fitted by the charge balance equation to accurately determine the donor level and corresponding donor concentration as well as the acceptor concentration for each sample. The measured donor levels were found to vary from sample to sample and there is evidence from the results that the variations are related to the differing growth conditions of the layers. The mobility data was also fitted to establish the dominant electron scattering mechanisms in the layers. The dominant scattering mechanisms were found to vary from sample to sample. For most of the layers studied, the dominant scattering mechanism was found to be both the ionised impurity scattering at low temperatures (20 – 100 K) and grain boundary scattering at higher temperatures (100 – 300 K). The effects of exposing the ZnO layers to hydrogen plasma were also investigated by the temperature dependent Hall-effect technique. Findings indicate that hydrogen is readily incorporated in ZnO, leading always to an increased carrier concentration. It was further noted that incorporating hydrogen into ZnO in some layers increased the mobility while in other layers it caused a decrease in the mobility. The hydrogenated samples were subsequently annealed at 600 °C for 1 hour in argon ambient resulting in the carrier concentration reducing to its original value. This effect is attributed to hydrogen diffusing out of ZnO.

An investigation of a pulsed Hg arc has been undertaken to test the relation V α I°⁴ between the voltage and current of an arc discharge. Although the experimental V-I characteristic exhibited this tendency, further considerations strongly indicated that the agreement between theory and experiment was probably a coincidence. The Paschen breakdown curve was determined, and together with simultaneous measurements of the current and voltage, it was possible to measure the average column field strength as a function of current. As a result of an unexpected feature of the apparatus, namely an inherent motion of the electrodes, the voltage waveform could be used to obtain an approximate measurement of the combined thickness of the anode and cathode falls df, and also the average field strength in these regions Ef. The measurements df = 3x10⁻⁶ cm, and Ef = 2.4x10⁶ volt/om appear to be in agreement with the field emission theory. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The d-c. and a-c. characteristics of p-n-p diodes were measured and interpreted on the basis of present theories. The equivalent parallel capacitance of these diodes was found to decrease as (f)⁻³/₂ at high frequencies in accordance with diffusion theory; from these measurements the lifetime of a hole in the base was estimated to be about 10 microseconds. The current fluctuations in the diode were measured by comparing them with a standard noise diode, and the results represented as a shunt noise current generator. From the frequency spectrum of the noise it was deduced that it consisted mainly of excess or 1/f noise except at low currents and high frequencies, and here the results were interpreted as a combination of shot and thermal noise. The deduced hot carrier temperature was compared with the theoretical values of Shockley and poor agreement was obtained, indicating inadequacy of the present theory. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Two possible ionospheric electric currents for Pi2 micropulsations are investigated and tested against data collected from a meridian chain of stations in Saskatewan. The electric coupling between the ionosphere and the magnetosphere under disturbed magnetospheric conditions is believed to be the cause of the Pi2 generation and propagation. The LC circuit analogy is first used to model this interaction, the source of energy lying in the magnetospheric equatorial plane. Secondly, the possibility of an ionospheric electric impulse imparted to a field-aligned current under the conditions of brightening of aurora is considered. It is found experimentally that the Pi2 originates possibly from these two source regions: the characteristics of a resonant LC oscillation expanding symmetrically to the west and to the east of the magnetospheric potential source are observed, as well a strong toroidal field existing and possibly originating in the ionosphere. It is suggested that optical data in conjunction with auroral radar echo and satellite data be necessary to confirm a future mathematical development of these possible Pi2 generation and propagation models. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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LD2668 .T4 1941 S55 / Master of Science

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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Co-Chair: Dr. Jianmin Qu; Committee Co-Chair: Dr. Mohammed Cherkaoui; Committee Member: Dr. Christophe Giraud-Audine; Committee Member: Dr. Nico Declercq. Part of the SMARTech Electronic Thesis and Dissertation Collection.

published_or_final_version / Physics / Master / Master of Philosophy