Oxygen Stoichiometry Engineering in P‐Type NiOx for High‐Performance NiO/Ga2O3 Heterostructure p–n Diode

P‐type NiO x is employed for the fabrication of NiO/Ga 2 O 3 p –n diode. Addressing the challenge of low hole mobility in NiO x , an extensive investigation into the impact of oxygen stoichiometry engineering in NiO x is conducted. The meticulous optimization of the O 2 /Ar ratio to 30% during the sputtering process results in significant improvements, notably achieving enhanced hole mobility of 1.61 cm 2 V −1 s. It leads to a low specific on‐resistance of 2.79 mΩ cm 2 and a high rectification ratio of ≈10 11 , underscoring the efficacy of recombination transport mechanism driven by enhanced hole mobility. Detailed band alignment analysis between NiO x and Ga 2 O 3 reveals a small band offset, with a valence band offset of 2.47 eV and a conduction band offset of 1.70 eV. It suggests a tailored modification of band alignment through the engineering the oxygen stoichiometry in NiO x , facilitating enhanced recombination conduction. The device exhibits a superior breakdown voltage ( V b ) of 2780 V and a notable Baliga's figure of merit (BFOM) of 2.77 GW cm −2 , surpassing the SiC unipolar figure of merit. The insights gained from this work are expected to inform future designs and optimizations of high‐performance Ga 2 O 3 electronic devices.