Leakage current and rectification behavior of Au / TiO₂ / GaN junctions with TiO₂ interlayer oxygen deposition pressure

Au/TiO₂/GaN junctions with a TiO₂ interlayer were deposited at various oxygen pressures from 5 mTorr to 80 mTorr, and their surface, microstructural, and electrical properties were investigated. Compared with a single 5 μm-Si-doped GaN film on an (0001) Al₂O₃ substrate, the 0.2 μm-Si-doped GaN film with an undoped GaN buffer layer demonstrated improved properties for the application to metal/semiconductor junctions. Atomic force microscope and tunneling electron microscope measurements suggested that the TiO₂ interlayer deposited at room temperature exhibited a distinctive change above the oxygen deposition pressure of 40 mTorr. In contrast to the small rectification ratio of 10¹-10² for Au/GaN junctions, the Au/TiO₂/GaN junctions with the TiO₂ interlayers displayed a large rectification ratio of 10⁶-10⁷ when the oxygen pressure during the deposition of TiO₂ interlayer was maintained at 40 mTorr. These results suggest that the leakage current and the rectification behavior in a metal/oxide/semiconductor junction can be effectively controlled using the oxygen deposition pressure for an oxide interlayer.