Publications

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Gd2O3 films were prepared on (0001)-oriented AlxGa1-xN (0≤x≤0.67) thin film substrates via reactive molecular-beam epitaxy. X-ray diffraction revealed that these films possessed the cubic bixbyite structure regardless of substrate composition and were all 111-oriented with in-plane rotations to account for the symmetry difference between the oxide film and nitride epilayer. Valence band offsets were characterized by X-ray photoelectron spectroscopy and were determined to be 0.41±0.02eV, 0.17±0.02eV, and 0.06±0.03eV at the Gd2O3/AlxGa1-xN interfaces for x=0, 0.28, and 0.67, respectively.

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There is currently a big thrust for integrating renewable resources to the electric grid. With increasing variable generation the need for energy storage devices has escalated. Traditional storage devices have bulky 60 Hz transformer to provide the electrical isolation from the grid. But, with the advent of advanced magnetic materials, power electronic topologies with high frequency link transformers are being researched. These systems have high power density and can be quickly dispatched for remote installations. This paper presents the design of the energy storage system consisting of the three phase rectifier and bi-directional dual active bride converter. It presents a methodology to optimize the switching frequency of the dual active bridge converter by minimizing the volume of the transformer and the total losses in the system. Frequency dependent and independent terms are aggregated and minimized over the range of switching frequency.

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This paper reports on trap-related shifts of the transfer curve and threshold voltage of power AlGaN/GaN HEMTs under switched bias operating life and reverse and forward DC bias stress. Opposite polarity threshold voltage shifts at room temperature under operating life and reverse bias stress conditions can be explained by means of drain current transient measurements under reverse bias stress conditions. A proposed model to explain the trapping/de-trapping behavior under different stress conditions is described and highlights the critical role of the electric field. Experimental evidence of the importance of the role of the electric field is seen in reduced parametric shift by improving the field plate design. © 2014 IEEE.

A method for extracting interface trap density (DIT) from subthreshold I-V characteristics is used to analyze data on a SiC MOSFET stressed for thirty minutes at 175°C with a gate bias of-20 V. Without knowing the channel doping, the change in DIT can be calculated when referenced to an energy level correlated with the threshold voltage. © 2014 IEEE.

Northern Arizona University (NAU) and the Southwestern Indian Polytechnic Institute (SIPI) conducted a pre- feasibility study for utility-scale solar power on the Jemez Pueblo in New Mexico. Student groups at NAU and SIPI analyzed four different 40-MW solar power projects to understand whether or not such plants built on tribal lands are technically and financially feasible. The NREL System Advisor Model (SAM) was employed to analyze the following four alternatives: fixed, horizontal-axis photovoltaic (PV); fixed, tilted-at-latitude PV; horizontal, single-axis tracking PV; and a solar-thermal "power tower" plant. Under supervision from faculty, the student teams predicted the energy production and net present value for the four options. This paper presents details describing the solar power plants analyzed, the results of the SAM analyses, and a sensitivity analysis of the predicted performance to key input variables. Overall, solar power plants on the Jemez Pueblo lands appear to pass the test for financial feasibility.

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