Gallium Oxide Heterojunction Diodes for 400 °C High‐Temperature Applications

β‐Ga2O3‐based semiconductor devices are expected to have significantly improved high‐power and high‐temperature performance due to its ultrawide bandgap of close to 5 eV. However, the high‐temperature operation of these ultrawide‐bandgap devices is usually limited by the relatively low 1–2 eV built‐in potential at the Schottky barrier with most high‐work‐function metals. Herein, heterojunction p‐NiO/n‐β‐Ga2O3 diodes fabrication and optimization for high‐temperature device applications are reported, demonstrating a current rectification ratio (ION/IOFF) of more than 106 at 410 °C. The NiO heterojunction diode can achieve higher turn‐on (VON) voltage and lower reverse leakage current compared to the Ni‐based Schottky diode fabricated on the same single‐crystal β‐Ga2O3 substrate, despite charge transport dominated by interfacial recombination. Electrical characterization and device modeling show that these advantages are due to a higher built‐in potential and additional band offset. These results suggest that heterojunction p–n diodes based on β‐Ga2O3 can significantly improve high‐temperature electronic device and sensor performance.