Vertical GaN Schottky barrier diodes (SBDs) are promising for high-voltage and high-efficiency power electronics, but their breakdown voltage is often limited by electric-field crowding at the Schottky anode edge. Conventional edge-termination technologies commonly involve ion implantation, high-temperature annealing, or complex fabrication processes. In this work, sputtered p-type NiO floating field rings (FFRs) are introduced as a low-temperature and implantation-free edge-termination scheme for vertical GaN SBDs. The p-NiO FFRs were formed by radio-frequency magnetron sputtering at room temperature followed by lift-off patterning. Reference SBDs without FFRs and p-NiO FFR-terminated SBDs were fabricated for comparison. Their forward and reverse current–voltage characteristics were measured to evaluate the conduction and blocking performance. Separate p-NiO/n-GaN test structures were also fabricated to characterize the electrical behavior of the heterojunction, while frequency-dependent capacitance–voltage measurements were performed to investigate the interface-related charge response. In addition, two-dimensional TCAD simulations were carried out to clarify the influence of the p-NiO FFRs on the electric-field distribution.
The reference SBD exhibits a breakdown voltage of approximately 300 V, whereas the p-NiO FFR-terminated SBD achieves a breakdown voltage of 830 V, corresponding to a 2.7-fold enhancement. Meanwhile, the terminated device maintains a low forward voltage of 0.71 V at 100 A/cm², a specific on-resistance of 1.2 mΩ·cm², and an on/off current ratio of approximately 10¹¹. TCAD simulations show that the electric field in the reference device is strongly concentrated at the Schottky anode edge, thereby limiting the reverse blocking capability. After introducing the p-NiO FFRs, the reverse-bias potential drop is redistributed from the anode edge to the successive FFR edges, thereby reducing the peak electric field at the anode periphery and extending the high-field region toward the outer termination region. The rectifying characteristics of the p-NiO/n-GaN test structures confirm the formation of a functional heterojunction, while the frequency-dependent capacitance characteristics indicate an interface-related charge response. These results demonstrate that room temperature sputtered p-NiO FFRs can effectively suppress electric-field crowding and improve the reverse blocking capability of vertical GaN SBDs without significantly degrading their forward conduction performance. The proposed structure provides a simple, low-thermal-budget, and implantation-free termination approach for vertical GaN power rectifiers.