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.