| Summary: | 碩士 === 國立臺灣大學 === 電子工程學研究所 === 104 === In this thesis, we focus on developing enhancement-mode operation devices. Instead of using conventional fluorine plasma treatment underneath the gate or growing p-type GaN or p-type AlGaN over the AlGaN barrier, we use fin structures, hoping to make threshold voltages shift to positive values by better controllability of fin structures. In chapter one, we simply introduce the motivation of our research, basic properties of GaN, operation of High Electron Mobility Transistor (HEMT), and experimental setup. In chapter two, we investigate the effect of fin structures on threshold voltages and on/off current density. We observe that by shrinking the fin width from 6μm to 2μm, threshold voltage and DIBL shift from -3.62V to -2.9V and 52.16mV/V to 21mV/V, respectively. Short channel effects are improved by fin structures. From the result of chapter two, we fabricate MOSFinHEMT and nano-scale FinHEMT by adopting atomic layer deposition and e-beam lithography, hoping to fabricate high current enhancement-mode device by combining the advantages brought from fin structures and increased applied gate voltages. By shrinking the fin width below 200nm, threshold voltage shifts from -3.33V to -0.48V. Although threshold voltage still is less than 0V, the threshold voltage shift is larger than that from planar device to 2μm-fin-width device. In chapter four, we applied the fabrication process of last two chapter on large area high current power devices. In order to obtain high current operation, we adopt planar structure and discuss the reasons behind poor off-state performance and poor controllability of large area devices. In chapter five, we summarize and make conclusions of our thesis.
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