Optically-switched integrated circuit power converters for high-temperature operation

The topic of this doctoral dissertation deals with new concepts of integrated power electronic circuits on wide bandgap semiconductors which are not possible in the standard widespread silicon technology. A novel architecture for a monolithic integrated circuit of a low-voltage/high-current to high-voltage/low-current DC/DC converter has been proposed and investigated. This circuit consists of an optically switched inverter and a “Cockroft-Walton” type voltage multiplier. Both theoretical and experimental studies have been performed on versions of the circuit that were fabricated on single-crystal semi-insulating gallium arsenide and high resistivity polycrystalline diamond.; In the course of this work a very high temperature rapid diffusion technique was conceived and investigated for doping polycrystalline diamond with boron. A prototype experimental setup for this procedure was constructed to provide temperatures exceeding 1700°C for time intervals up to 10 minutes in a high-vacuum chamber. P-type borondoped diamond layers obtained by this method exhibited carrier concentrations up to 1018 cm-3, with sheet resistances of 323–257 Ohm/square and average diffusion length of 0.5–0.6 μm. These characteristics were found to be superior to those found in the previously published literature based on diffusion methods. This procedure was subsequently adopted for the fabrication of the diamond-based integrated circuits.; The carrier dynamics in polycrystalline diamond were theoretically modeled by taking into account the effects of non-uniform doping profiles, carrier trapping and scattering at the grain boundaries, at high voltages and high temperatures. This model predicted the formation of a quasi-insulating layer in diffusion-doped polycrystalline diamond. In this layer the charge carriers are characterized by very low mobility resulting in an increase of resistivity of the conducting layer. On the basis of this theory, an analytical model of the optically switched inverter operation was assembled and investigated. This theory predicted a maximum operating temperature for the inverter to be about 400°C at a maximum input voltage of 300V. An optimized design of a 1.5 kV optically switched inverter was then simulated. Voltage multiplier circuits were simulated in SPICE using the measured characteristics of fabricated devices.; Complete characterization of the optically switched inverters was restricted by the intensity and wavelength range of the available optical sources. Best results were obtained with a mercury-arc light source yielding practical inverter gains of 5% for the diamond-based circuits and 50% for the GaAs-based circuits at room temperature. The maximum operating temperatures for these circuits were experimentally found to be 394°C for the diamond-based circuits and 154°C for the GaAs-based circuits. However, actual characterization of this was not possible without a high-intensity EUV source. Characterizations of the ten-stage GaAs-based voltage multipliers demonstrated multiplication factors up to 16.7. Using data from diamond-based devices in SPICE simulation of diamond-based voltage multiplier circuits showed that multiplication factors as high as 15.5 for a ten-stage circuits should be possible.