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A film which is optically transparent and electrically conductive is difficult to come by but can be realized in ways such as doping an oxidized film or by oxidizing a metallic film resulting in what is known as a transparent conducting oxide (TCO). TCO's have many important uses in electronics, especially as the top contact in to solar cells where efficient transmission of light and low electrical resistivity allow for higher efficiency solar cells and as the gate contact in AlGaN/GaN HFET's allowing for optical characterization of the subsurface transistor properties. Because these devices rely heavily on the characteristics of its material interfaces, a detailed analysis should be done to investigate the electrical effects of implementing a TCO. In this work, the electrical characterization of ruthenium dioxide (RuO₂) Schottky contacts to gallium nitride (GaN) formed by evaporating ruthenium with a subsequent open-air annealing is presented. The results gathered from the current-voltage-temperature and the capacitance-voltage relationships were compared to ruthenium (Ru) on GaN and platinum (Pt) on GaN. Additionally, the measurement and analysis procedure was qualified on a similar structure of nickel on GaAs due to its well-behave nature and presence in the literature. The results indicate that an inhomogeneous Gaussian distribution of barrier heights exists at the RuO₂/GaN interface with an increase of 83meV in the mean barrier height when compared to Ru/GaN. / Master of Science

The decline of easily accessible reserves pushes the oil and gas industry to explore deeper wells, where the ambient temperature often exceeds 210 °C. The need for high temperature operation, combined with the need for real-time data logging has created a growing demand for robust, high temperature RF electronics. This thesis presents the design of an intermediate frequency (IF) variable gain amplifier (VGA) for downhole communications, which can operate up to an ambient temperature of 230 °C. The proposed VGA is designed using 0.25 μm GaN on SiC high electron mobility transistor (HEMT) technology. Measured results at 230 °C show that the VGA has a peak gain of 27dB at center frequency of 97.5 MHz, and a gain control range of 29.4 dB. At maximum gain, the input P1dB is -11.57 dBm at 230 °C (-3.63 dBm at 25 °C). Input return loss is below 19 dB, and output return loss is below 12 dB across the entire gain control range from 25 °C to 230 °C. The variation with temperature (25 °C to 230 °C) is 1 dB for maximum gain, and 4.7 dB for gain control range. The total power dissipation is 176 mW for maximum gain at 230 °C. / Master of Science