Effects of plasma treatments on Ohmic formation for N polarity of n+-GaN substrates

In this Letter, we demonstrate low-resistance Ohmic contacts on N-polar GaN via plasma surface treatment, systematically investigating optimization mechanisms. O2 plasma treatment induces the formation of an ultrathin (∼2 nm) oxide interlayer at the metal–semiconductor interface, which serves dual roles. It prevents direct metal–GaN interaction and reconstructs surface states through oxygen passivation. This dual functionality significantly mitigates Fermi-level pinning and reduces the effective Schottky barrier height. These interfacial modifications yield a remarkably low specific contact resistivity (ρc) of 3.84 × 10−6 Ω cm2, as measured by the multi-ring circular transmission line model. This plasma-based strategy establishes a scalable approach for high-performance Ohmic contacts in GaN devices.