Low defect density and small $I−V$ curve hysteresis in NiO/β-Ga₂O₃ pn diode with a high PFOM of 0.65 GW/cm²

In this Letter, we report a high-performance NiO/β-Ga₂O₃ pn heterojunction diode with an optimized interface by annealing. The electrical characteristics of the pn diode without annealing (PND) and with annealing (APND) are studied systematically. The APND device has a lower specific on-resistance of 4.1 mΩ cm², compared to that of the PND, 5.4 mΩ cm². Moreover, for the APND, a high breakdown voltage of 1630 V with lower leakage current is achieved, which is 730 V higher than that of the PND. The enhanced electrical performance of the APND leads to a record high power figure of merit of 0.65 GW/cm² in Ga₂O₃-based pn diodes, which is among the best reported results in Ga₂O₃ power devices. In addition, the interface trap density of the diode decreases from 1.04 × 10¹² to 1.33 × 10¹¹ eV⁻¹ cm⁻² after annealing, contributing to much lower hysteresis. Simultaneously, the ideality factor $n$ for the APND is steady at elevated temperatures due to the stable interface. The results of $C−V$ characteristics reveal the bulk defects inside the nickel oxide film grown by sputtering, which are calculated by high- and low-frequency capacitance methods. X-ray photoelectron spectroscopy of NiO illustrates the reasons for the changes in the concentration of holes and defects in the film before and after annealing. This work paves the way for further improving the performance of Ga₂O₃ diode via interface engineering.