Deep mesa is an effective edge termination widely deployed in high-voltage power devices. However, its effectiveness requires the minimal distance between mesa and electrode edge and is susceptible to charges in the dielectric passivation, posing challenges in practical implementation. Here, we propose a deep mesa termination encapsulated by p-type materials, which functions as a reduced-surface-field (RESURF) structure and enables a wide design and process window. We demonstrate the RESURF-mesa design in vertical Ga3O3 diodes. In this design, a 5 μm deep mesa, which is intentionally not aligned with the anode edge, is encapsulated by p-type nickel oxide (NiO). This termination has been applied to devices on three Ga2O3 wafers with epitaxial doping concentrations ranging from 1.2 × 1016 to 5 × 1016 cm−3, enabling an average one-dimensional junction field of 4.2–4.4 MV/cm in all wafers. Additionally, the diode with 1.2 × 1016 cm−3 doping achieves a specific on-resistance (RON,sp) of 4.05 mΩ·cm2 and a breakdown voltage of 3214 V, resulting in a power figure of merit of 2.55 GW/cm2, which is among the highest in multi-kilovolt β-Ga2O3 diodes. The above results demonstrate the RESURF-mesa termination as a versatile and effective solution for wide bandgap and ultra-wide bandgap power devices.
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2025
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