Breakdown up to 13.5 kV in NiO/β-Ga₂O₃ Vertical Heterojunction Rectifiers

Vertical heterojunction NiO/β n-Ga₂O/n⁺ Ga₂O₃ rectifiers with 100 μm diameter fabricated on ∼17-18 μm thick drift layers with carrier concentration 8.8 × 10¹⁵ cm⁻³ and employing simple dual-layer PECVD SiNx/SiO₂ edge termination demonstrate breakdown voltages (V_B) up to 13.5 kV, on-voltage (V_ON) of ∼2.2 V and on-state resistance R_ON of 11.1-12 mΩ.cm². Without edge termination, the maximum V_B was 7.9 kV. The average critical breakdown field in heterojunctions was ∼7.4-9.4 MV. cm⁻¹, within the reported theoretical value range from 8-15 MV.cm⁻¹ for β-Ga₂O_3. For large area (1 mm diameter) heterojunction deives, the maximum V_B was 7.2 kV with optimized edge termination and 3.9 kV without edge termination. The associated maximum power figure-of-merit, V_B²/R_ON is 15.2 GW·cm⁻² for small area devices and 0.65 GW.cm⁻² for large area devices. By sharp contrast, small area Schottky rectifiers concurrently fabricated on the same drift layers had maximum V_B of 3.6 kV with edge termination and 2.7 kV without edge termination, but lower V_ON of 0.71-0.75 V. The average critical breakdown field in these devices was in the range 1.9-2.7 MV. cm⁻¹, showing the importance of both the heterojunction and edge termination. Transmission electron microscopy showed an absence of lattice damage between the PECVD and sputtered films within the device and the underlying epitaxial Ga₂O₃. The key advances are thicker, lower doped drift layers and optimization of edge termination design and deposition processes.