Vertical geometry NiO/Ga2O3 heterojunction (HJ) rectifiers and Ni/Au Schottky rectifiers fabricated on the same wafer and each with the same diameter (100 μm) were operated at 77–473 K to compare their capabilities in space-like environments. The HJ rectifiers suffer a 4-order reduction in forward current at 77 K due to the freeze-out of acceptors in the NiO, leading to MIS-type operation. By sharp contrast, the Schottky rectifiers have higher forward current and lower on-resistance at 77 K compared to 298 K due to improved carrier mobility. The on/off ratio of Schottky rectifiers at 77 K becomes similar to HJ rectifiers at 298–473 K. The reverse recovery time of Schottky rectifiers is reduced from 20 ns at 273 K to 16 ns at 77 K, while HJ rectifiers cannot be switched at this temperature. While the latter are superior for high-temperature applications, the former are better suited to cryogenic operation.
