p-NiO/LiNiO-GaN heterojunctions: a potential alternative to p-GaN for advanced devices

In this work, we introduce a p-NiO/LiNiO stack grown via low-temperature deposition processes, offering an effective alternative for creating localized p-type regions in GaN devices. This stack combines a high hole concentration p-NiO film ([h] = 2 × 1019 cm-3) with an epitaxially crystalline p-LiNiO film, resulting in a high-quality p-type layer that can be flexibly deposited and patterned on GaN devices. Here, we investigate the transport and breakdown properties of the p-NiO/LiNiO-GaN heterojunction by fabricating a p-NiO/LiNiO-GaN PiN diode. The PiN diode exhibited excellent electrical performance, including a low turn-on voltage (VON) of 1.7 V, a low specific on-state resistance (RON, sp) of 1.15 mΩ·cm2, and a high breakdown voltage (BV) exceeding 1000 V, comparable to those achieved with epitaxial GaN homojunctions. These results highlight the potential of utilizing conductive and compatible p-NiO/LiNiO stacks to replace p-GaN for high-quality localized p-n junctions, simplifying the manufacturability of GaN-based devices and enabling advanced device concepts where p-GaN is challenging to be implemented.