We have achieved both low contact resistance and smooth surface morphology by using Ti∕Al∕Nb∕Au formed on an Al0.3Ga0.7N∕GaN heterostructure. A low contact resistance of less than 0.6Ω∕mm was reproducibly recorded after thermal treatment with a wide range of annealing temperature from 830 to 1000°C and annealing time from 10 to 300s. It was found that root-mean square surface roughness of under 35nm was obtained with all the annealing conditions investigated. In consideration of surface roughness and reproducibility, the most suitable annealing condition was 850°C for 100s, which leads to a contact resistance and a specific contact resistivity of 0.48Ω∕mm and 5×10−6Ω∕cm2, respectively.
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