Two-step oxygen treatments for low-resistance ohmic contacts on p-NiO

As an important p-type wide-bandgap oxide semiconductor, NiO exhibits promising prospects for application in wide-bandgap power devices. However, owing to its high work function, strong Fermi-level pinning effect, and large hole injection barrier, it is challenging to realize low-resistance ohmic contacts on p-NiO. In this work, a synergistic surface engineering strategy combining oxygen plasma treatment (OPT) and oxygen rapid annealing (ORA) is proposed to optimize the Ni/NiO ohmic contact. Mechanistic studies demonstrate that this synergistic treatment process can introduce interstitial oxygen into the NiO surface layer to increase the hole concentration, narrow the interfacial depletion width, and enhance carrier tunneling transport. Meanwhile, it can effectively reduce the interface state density, thereby alleviating Fermi-level pinning, lowering the surface barrier, and significantly improving interface uniformity and stability. After the OPT+ORA treatment, the specific contact resistivity ρc of Ni/NiO is reduced from 2.55 × 10−3 to 8.01 × 10−5 Ω cm2. By applying this process to a p-NiO/n-Ga2O3 heterojunction diode, the specific on-resistance RON,sp decreases from 5.28 to 3.08 mΩ cm2. This approach provides an effective pathway for achieving low-resistance ohmic contacts on p-type NiO and realizing high-performance NiO-based wide-bandgap power devices.