Improving electrical properties of metal–semiconductor contact on Al-rich n-AlGaN by multi-step annealing

N-type Ohmic contact on Al-rich AlGaN has garnered special attention, thanks to its crucial impact on the performance of deep ultraviolet devices, which are experiencing a surge in demand. However, the Ohmic contact is still suffering from the poor matching of energy band at metal–semiconductor interface. In this work, multi-step annealing is proposed to facilitate the Ohmic contact between Ti/Al/Ni/Au electrodes and n-AlGaN with Al composition higher than 60%. It is found that the first low-temperature annealing is capable to effectively suppress the excessive diffusion of Ti metal, which enables the generation of low-work function TiN film on the n-AlGaN, while the subsequent high-temperature annealing is adopted to provide an adequate driving force for breaking the N-related bonds with high bond energy, which gives rise to a large number of N-vacancies on the surface of n-AlGaN and, consequently, contributes to a high electron concentration. Thanks to the aforementioned two processes, the electron tunneling barrier height and width can be reduced, thus promoting the formation of Ohmic contact on etched n-Al0.65Ga0.35N, with a specific contact resistivity is as low as 2.58 × 10−4 Ω cm2.