β-Ga₂O₃ vertical heterojunction barrier Schottky diodes terminated with p-NiO field limiting rings

In this Letter, high-performance β-Ga₂O₃ vertical heterojunction barrier Schottky (HJBS) diodes have been demonstrated together with the investigation of reverse leakage mechanisms. In HJBS configurations, NiO/β-Ga₂O₃ p-n heterojunctions and p-NiO field limiting rings (FLRs) are implemented by using a reactive sputtering technique at room temperature without intentional etching damages. Determined from the temperature-dependent current-voltage characteristics, the reverse leakage mechanism of the HJBS diode is identified to be Poole-Frenkel emission through localized trap sates with an energy level of E_C-0.72 eV. With an uniform FLR width/spacing of 2 μm in HJBS, a maximum breakdown voltage (BV) of 1.89 kV and a specific on-resistance (R_on,sp) of 7.7 mΩ·cm² are achieved, yielding a high Baliga's figure-of-merit (FOM, BV²/R_on,sp) of 0.46 GW/cm². The electric field simulation and statistical experimental facts indicate that the electric field crowding effect at device edges is greatly suppressed by the shrinkage of p-NiO FLR spacing, and the capability of sustaining high BV is enhanced by the NiO/β-Ga₂O₃ bipolar structure, both of which contribute to the improved device performance. This work makes a significant step to achieve high performance β-Ga₂O₃ power devices by implementing alternative bipolar structures to overcome the difficulty in p-type β-Ga₂O₃.