Abstract: The ultra-wide bandgap semiconductor β-Ga₂O₃ is a promising semiconductor material for manufacturing high power and high efficiency power device due to its high critical breakdown field and low on-state loss. However, the actual performance of existing β-Ga₂O₃ diode is far from the theoretical value. It is urgent to develop high efficiency edge termination techniques to suppress the peak electric field and improve the breakdown voltage. In this paper, the mesa termination technique for NiO/β-Ga₂O₃ heterojunction diode were systematically studied, and the performance of the devices with different etching depths were compared, including 0, 0.37, 0.74, 1.11 μm. The breakdown voltage of mesa termination diode first increases with the increase of etching depth, and then degrades due to the accumulation of the etching damage. The results show that at the etching depth of 1.11 μm, the breakdown voltage increases from 970 V to 2 600 V, and the on-state resistance slightly increases from 6.43 mΩ·cm² to 7.38 mΩ·cm². The electric field distribution of the device was studied by simulation, and it indicates that the mesa termination transfers the peak electric field from the anode edge to the etching corner, and greatly suppress the electric field. The post-annealing after etching significantly reduces the leakage current of device. The leakage current of device is only 4×10^-7 A/cm² under -2 000 V, while the breakdown voltage is not changed (2 625 V). The on-state resistance reduce to 6.96 mΩ·cm², yielding a high power figure of merit of 0.99 GW/cm². This work provides a new approach for the design of terminations for high breakdown voltage and low leakage β-Ga₂O₃ diodes.

Key words: β-Ga₂O₃, NiO heterojunction diode, mesa termination, annealing, breakdown voltage