Enhanced breakdown performance on GaN vertical diodes through intrinsic polarization fields and extrinsic p-oxides

Vertical Gallium Nitride (GaN) power devices are highly promising for revolutionizing high-voltage electronics, yet unlocking their full potential requires addressing critical challenges in electric-field management and fabrication complexity. Specifically, mitigating peak electric fields at the metal/semiconductor interface and at the metal contact edge is essential to suppress leakage current and prevent premature device breakdown. Primarily targeting this topic, this thesis explores the adaptation of two concepts-polarization engineering and selective p-doping-which are key breakthroughs for high-performance lateral GaN transistors, to vertical GaN diodes to manage electric fields and improve GaN diode breakdown voltages (BV) with simple device designs. First, the concept of polarization engineering is introduced to manage the electric field intrinsically at the Schottky interface. By inserting an ultra-thin p-InGaN interlayer between the Schottky contact and the GaN drift region, we successfully introduced a strong polarization field that counteracts the external electric field to improve breakdown performance without degrading forward conduction, effectively mitigating the trade-off between breakdown voltage and on-resistance. Second, to address the limitations of selective p-doping in GaN for advanced power devices, we introduced a p-NiO/LiNiO stack as a high-quality, fabrication-friendly alternative to p-GaN. Grown via low-temperature deposition processes, this oxide stack combines the high hole concentration of NiO and the better film quality of LiNiO, with increased device fabrication flexibility and design space. We demonstrated its effectiveness by fabricating a high-performance heterojunction p-NiO/LiNiO-GaN PiN diode. Based on these, we integrated the intrinsic polarization fields and the extrinsic p-oxides into one vertical GaN SBD. In this design, the p-InGaN layer is grown beneath the Schottky contact, which effectively shields the peaking electric fields from the Schottky interface, while conductive p-NiO/LiNiO regions are selectively deposited at the Schottky contact edge and serve as junction termination extensions (JTEs) to mitigate electric field crowding. These simple designs, based on effective electric-field management, resulted in state-of-the-art GaN Schottky diode performance. In summary, this thesis demonstrates the power of intrinsic polarization engineering and extrinsic oxide-based selective p-doping in redistributing/managing the peak electric fields in vertical GaN devices, with simple device designs and straightforward fabrication processes, pushing device performance closer to the material limits.