ECCS-EPSRC: Nitride Super-Junction HEMTs for Robust, Efficient, Fast Power Switching

Gallium nitride (GaN) high electron mobility transistors (HEMTs) are widely perceived as the next-generation power devices for electrical energy processing in electric vehicles, electricity grid, and data centers, among other applications. Although low-voltage GaN HEMTs have been commercialized recently by companies such as GaN Systems, Navitas, Infineon and EPC, their penetration into the $35 billion power device market is still slow, mainly due to their limited reliability and robustness. In particular the lack of capability to dissipate surge energy when in breakdown is one of the main shortcomings of Gallium nitride power devices. The limited robustness, in turn, requires significant over-engineering making
the performance of current GaN devices less attractive.

In this project we aim to develop a superjunction GaN heterojunction transistor based on selective-area growth of an Aluminum Gallium-Nitride layer, nearly defect-free embedding, adjacent to the existing two dimensional electron gas to allow for charge compensation. The electron concentration of the two dimensional gas can be increased by a factor of 3-5X, when compared to a standard device, resulting in a significant reduction of chip size, wafer cost per device, device capacitance, and switching losses. Meanwhile, the peak electric field is moved from device surface into the bulk of the transistor allowing for an increased robustness during breakdown. The proposed superjunction Gallium Nitride device could enable an unprecedented enhancement in switching frequency, power conversion efficiency, and surge robustness in power systems.

We assembled a strong consortium with complementary expertise comprising both US and UK researchers with a strong track record of collaboration. Florin Udrea at Cambridge University, UK, is a pioneer in power devices and was involved in early work on superjunction devices. Yuhao Zhang at Virginia Tech, US has significant expertise in nitride processing and growth technologies in III-V materials. Han Wang at University of Southern California, US has dedicated expertise in material and device characterization This project will significantly expand the application space of nitride power transistors and revolutionize the landscape of medium and high-voltage power electronics. The developed technologies for selective area p-type doping can bring significant advancements in many other nitride devices. The knowledge on bulk-2D SJ will open the door for developing novel electronic and optoelectronics devices in other bulk and 2DEG materials.