Influences of GaN surface oxides on interface properties of metal/n-GaN Schottky structures are investigated by comparing I-V-T and C-V characteristics of the structures formed on intentionally oxidized and oxide-etched GaN surfaces. It is found that a thermal oxidation introduces little change of the ideality factor while it leads to a slight reduction of the Schottky barrier height (SBH), for the Ni/n-GaN structure. Slow current drift was below 0.1 within the range of 1-10{sup}4 sec. I-V-T characteristics showed that the inhomogenity of the SBH is comparable with that of the oxide-etched sample. On the other hand, an anodization of GaN surface lead to increase of the SBR up to 0.3 eV, owing to formation of a relatively thick oxide layer. The oxide-etched Au/n-Al{sub}0.2Ga{sub}0.8N sample with a selectively doped N{sub}D of 10{sup}18 cm{sup}(-3) order for HEMT structure represented a considerably reduced effective SBH at RT, because of a large leakage current due to the tunneling mechanism. Again, the annealing in N{sub}2 ambient is highly effective to improve characteristics of metal/n-AlGaN structures.
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