Ultralow Contact Resistivity of <0.13 Ω · mm for Normal Ti/Al/Ni/Au Ohmic Contact on Non-Recessed i-AlGaN/GaN

By utilizing a traditional Ti/Al/Ni/Au metal stack on i-AlGaN/GaN, we achieved an ultralow contact resistivity of $\lt 0.13~\Omega ~\cdot $ mm through a combined annealing process, which includes holding at $550~^{\circ }$ C for 20 s, followed by a 60-s annealing at $840~^{\circ }$ C with an optimized ramp-up rate of $10~^{\circ }$ C/s. The formation of TixAlyAuz alloy spikes directly contacting the 2DEG is identified as the primary mechanism for the ultralow contact resistance, which we attribute to the severity of Al transitioning into a molten state during the process.