CAREER: A New GaN-based Unit Cell for Highly Efficient Integrated Power Conversion

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The research objective of this Faculty Early Career Development (CAREER) Program award is to develop a very low loss power transistor with an integrated drive circuit for power conversion applications. The approach will use an innovative fabrication process to address issues with Gallium Nitride-based vertical transistors that have previously limited the technology from achieving superior performance and widespread adoption. A significant amount of energy is wasted as heat due to inefficient power conversion. The solution provided through this program will reduce or eliminate the wasted energy thereby effectively extending the lifetime of available energy resources. This energy savings will add to the global energy security and reduce greenhouse gas emissions. The educational and outreach components are aimed at fostering interest in Science, Technology, Engineering, and Mathematics (STEM) disciplines and developing scientific knowledge at the undergraduate and K-12 levels. These activities are focused on working with a diverse group of students particularly women and other underrepresented groups. Integration of the research and education will be achieved through workshops and classes dedicated to understanding semiconductor devices and build prototypes or models for their K-12 classrooms. Specific outreach goals include collaboration with K-8 girls through Engineering Adventure and Teacher College candidates through Engineers Serving Education. The educational goal is to continue building on a recently introduced coursework on power electronics and extend the knowledge on cutting edge technologies acquired through the research under this program.The unique polarization properties of the nitrogen polar orientation of Gallium nitride will be utilized for the first time to develop vertical transistors that require no interruptions during the growth of the structure. The reverse polarization field of the Aluminum Gallium Nitride/Gallium Nitride heterostructure is designed to block current in the transistor while providing a very conductive path for the current to flow in designated region. An on-state resistance below 1 mohm.cm2 is estimated from this novel transistor design and is set as a target in this program. Lack of an integrated gate driver has limited high switching speed and efficiency of power converters due to the deleterious effects of board interconnects and bond wire inductance. This innovation pushes the limits of power electronics to very high power densities with high efficiency delivered at high frequencies by first developing superior performance of nitride-based vertical transistors and then eliminating the limits placed on switching speed by trace inductance of bond wires and board interconnects by integrating the driver circuit based on lateral transistors on-chip. The scope of this research extends into both fundamental device research and application space where the device structures will be used to determine fundamental properties of the material including the first direct measurement of electron velocity in Gallium nitride. Finally the merit will be evident through new circuit architectures with increased efficiency and reduced form factor by enabling high efficiency power conversion at high frequencies.