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III-V materials such as indium arsenide (InAs) and gallium arsenide (GaAs) are increasingly used in electronic and photovoltaic devices. The extensive application of these materials may lead to release of III-V ionic species during semiconductor manufacturing or disposal of decommissioned devices into the environment. Although arsenic is recognized as an important contaminant due to its high toxicity, there is a lack of information about the toxic effects of indium and gallium ions. In this study, acute toxicity of As(III), As(V), In(III) and Ga(III) species was evaluated using two microbial assays testing for methanogenic activity and 02 uptake, as well as two bioassays targeting aquatic organisms, including the marine bacterium Aliivibrio fischeri (bioluminescence inhibition) and the crustacean Daphnia magna (mortality). The most noteworthy finding was that the toxicity is mostly impacted by the element tested. Secondarily, the toxicity of these species also depended on the bioassay target. In(III) and Ga(III) were not or only mildly toxic in the experiments. D. magna was the most sensitive organism for In(III) and Ga(III) with 50% lethal concentrations of 0.5 and 3.4 mM, respectively. On the other hand, As(III) and As(V) caused clear inhibitory effects, particularly in the methanogenic toxicity bioassay. The 50% inhibitory concentrations of both arsenic species towards methanogens were about 0.02 mM, which is lower than the regulated maximum allowable daily effluent discharge concentration (2.09 mg/L or 0.03 mM) for facilities manufacturing electronic components in the US. Overall, the results indicate that the ecotoxicity of In (III) and Ga(III) is much lower than that of the As species tested. This finding is important in filling the knowledge gap regarding the ecotoxicology of In and Ga.

Transport imaging is a SEM-based technique used to directly image the motion and recombination of charge in luminescent semiconductors, allowing for the extraction of transport parameters critical to device operation. In this thesis, transport imaging for 1D structures was initiated with work on sample preparation, modeling and initial characterization. One dimensional structures are being integrated into forefront electronics due to their inherent advantages in size, packing density and power consumption. In this work the one dimensional equation for steady state minority carrier recombination distribution solved for the Gaussian source is derived and results from numerical simulations are presented. The diameter of the SEM beam is determined experimentally allowing for accurate simulation parameters. Intensity and drift measurements on four batches of top-down wire structure samples, fabricated on a AlGaAs/GaAs/AlGaAs double heterostructure using a FIB, are presented. Significant decreases in luminescence in FIB exposed regions are reported. Spatial luminescence from single bottom-up GaN and ZnO nanowires deposited by metal initiated metal-organic CVD on Au and SiO2 substrates is imaged. CL spectra for GaN and ZnO, with peak intensities at 3.27 and 3.29 eV, are characterized. Finally, several suggestions for further research are offered including transport imaging on contacted bottom-up nanowires and a potential application of transport imaging to FIB damage characterization.

Master of Science / Department of Chemistry / Takashi Ito / Adsorption of a series of primarily substituted hydrocarbons (RX; C[subscript]18H[subscript]37PO(OH)[subscript]2 (ODPA), C[subscript]17H[subscript]35COOH, C[subscript]18H[subscript]37OH, C[subscript]18H[subscript]37NH[subscript]2 and C[subscript]18H[subscript]37SH) onto solid gallium substrates with and without UV/ozone treatment was studied using contact angle goniometry, spectroscopic ellipsometry and cyclic voltammetry (CV). UV/ozone treatment offered a hydrophilic surface (water contact angle ([theta][superscript]water) less than 10°), reflecting the formation of a surface oxide layer with the maximum thickness of ca. 1 nm and possibly the removal of surface contaminants. Upon immersion in a toluene solution of a RX, [theta][superscript]water increased due to adsorption of the RX onto gallium substrates. In particular, UV/ozone-treated gallium substrates (UV-Ga) immersed in an ODPA solution exhibited [theta][superscript]water close to 105°. The ellipsometric thickness of the adsorbed ODPA layer was ca. 2.4 nm and CV data measured in an acetonitrile solution showed significant inhibition of redox reaction on the substrate surface. These results indicate the formation of a densely-packed ODPA monolayer on UV-Ga. The coverage of a C[subscript]17H[subscript]35COOH layer adsorbed onto UV-Ga was lower, as shown by smaller [theta][superscript]water (ca. 99°), smaller ellipsometric thickness (ca. 1.3 nm) and smaller electrode reaction inhibition. Adsorption of the other RX onto UV-Ga was weaker, as indicated by smaller [theta][superscript]water (82-92°). ODPA did not strongly adsorb onto UV-untreated gallium substrates, suggesting that the ODPA adsorption mainly originates from hydrogen bond interaction of a phosphonate group with surface oxide. These results will provide a means for controlling the surface properties of oxide-coated gallium that play an essential role in monolayer conductivity measurements and electroanalytical applications.

Master of Science / Department of Electrical and Computer Engineering / Behrooz Mirafzal / Wide bandgap devices have gained increasing attention in the market of power electronics for their ability to perform even in harsh environments. The high voltage blocking and high temperature withstanding capabilities make them outperform existing Silicon devices. They are expected to find places in future traction systems, electric vehicles, LED lightning and renewable energy engineering systems. In spite of several other advantages later mentioned in this paper, WBG devices also face a few challenges which need to be addressed before they can be applied in large scale in industries. Electromagnetic interference and new requirements in packaging methods are some of the challenges being faced by WBG devices. After the commercialization of these devices, many experiments are being carried out to understand and validate their abilities and drawbacks. This paper summarizes the experimental results of various applications of mainly Silicon Carbide (SiC) and Gallium Nitride (GaN) power devices and also includes a section explaining the current challenges for their employment and improvements being made to overcome them.