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UBC Theses and Dissertations

Enhanced performance of p-GaN gate AlGaN/GaN high-electron-mobility transistors for power applications Zhou, Guangnan


Gallium nitride (GaN) possesses excellent physical properties, such as a high critical electric field, a high saturation velocity, a high electron mobility, and a good thermal stability. Due to these superior material properties, GaN-based high-electron-mobility transistors (HEMTs) have performances superior to their silicon (Si) counterparts. They can operate at higher voltages, currents, frequencies, and temperatures, making them ideal devices for the next-generation high-efficiency power converters applications, such as phone chargers, electric vehicles, data centers and renewable energy. For switching applications, normally-off transistors are required to provide adequate safety. Due to the positive and stable threshold voltage, p-GaN gate HEMT technology is the most promising candidate among many options of normally-off HEMTs. Meanwhile, there are still some problems to be addressed (e.g., low threshold voltage, low gate breakdown voltage, gate reliability) for the p-GaN gate technology. In this dissertation, we present a comprehensive study of p-GaN gate HEMTs, including the work on failure mechanisms and three different methods to enhance the device performance. Chapter 1 includes a background review for power devices, GaN material properties and basic AlGaN/GaN HEMT structures. In Chapter 2, a typical fabrication process and test methods for p-GaN gate HEMTs are described in detail. Chapter 3 demonstrates a novel measurement and analysis method to identify three different gate failure mechanisms. Based on the baseline process in Chapter 2 and the analysis method in Chapter 3, three different structures aimed at enhancing the p-GaN gate HEMTs’ electrical performance and reliability are demonstrated in Chapters 3 to 6, including metal/graphene gates, ultra-high-resistance Au/Ti/p-GaN junctions, and doping engineering. The three different methods have their unique strengths. Chapter 7 concludes this work and suggests some future directions.

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