Degradation mechanism of degenerate n-GaN ohmic contact induced by ion beam etching damage

The degradation of an n⁺⁺ GaN regrown ohmic contact in a MIS-HEMT device induced by ion beam etching (IBE) damages and relevant mechanisms have been studied. Abnormal I–V behaviors of the etched n⁺⁺ GaN were observed by the transfer length method using a Ti/Al/Ni/Au stack as the contact metal, and it can be recovered with the assistance of post-metallization rapid thermal annealing. According to further analysis, we speculate that the degradation of the ohmic contact originates from the preferential loss of nitrogen by IBE, which boosts the oxygen incorporation and formation of an oxide layer isolating the contact metal from the n⁺⁺ GaN.