High power III-nitride transistors for energy conversion

AlGaN/GaN Heterostucture Filed Effect Transistors (HFETs) are attractive as fast high power switches. The challenge of AlGaN/GaN power switch development lies in achieving both low dynamic ON-resistance and high breakdown voltages simultaneously in a device.; The present thesis shows the importance of parasitic air breakdown in determining breakdown voltages of these devices above 450 V and presents novel ways to achieve breakdown voltages as high as 1600 V on AlGaN/GaN HFETs having specific ON-resistance as low as 3.4 mO.cm2.; Mitigation of current collapse in high breakdown voltage AlGaN/GaN HFETs is generally achieved by passivating these devices with Silicon Nitride (SiN). SiN passivation results in huge increase of gate leakage in AlGaN/GaN HFETs decreasing breakdown voltages of these devices. Studies done to understand the nature of gate leakage increase after SiN passivation revealed that leakage increase is happening vertically through AlGaN buffer layer at drain side edge of gate. An overlapping gate structure over SiN passivation layer extending toward drain contact known as field plate was found to limit SiN induced gate leakage improving AlGaN/GaN HFET breakdown voltage. It was found that breakdown voltages above 450V in field plated devices are also limited by parasitic air breakdown. Silicon dioxide encapsulation, SiN passivation and Field plating of AlGaN/GaN HFETs was found to be a comprehensive design approach to having low ON-resistance high voltage III-Nitride switching devices working in air ambience for power converter applications.; The AlGaN/GaN HFET device rise time was measured to be 10 ns and fall time was 30 ns. These results prove the feasibility of using high voltage III-Nitride HFETs as low loss ultra-fast power converter switches.; Finally, the thesis introduces AlGaN/GaN HFETs as bidirectional power switches and presents a novel approach to achieving Bidirectional Power Switching functionality using AlGaN/GaN HFETs and for the first time presents experimental data showing power bidirectional capability of these devices.