Interface trap characterization of AlN/GaN heterostructure with Al₂O₃, HfO₂, and HfO₂/Al₂O₃ dielectrics

The interfacial properties of AlN/GaN heterostructures with different dielectric layers such as Al₂O₃, HfO₂, and HfO₂/Al₂O₃ prepared by atomic layer deposition were investigated. Interface state density versus energy level plots obtained from the Terman method revealed the peculiar peaks at ∼0.25 eV for the samples with Al₂O₃ and HfO₂/Al₂O₃ and at ∼0.52 eV for the sample with HfO₂, associated with nitrogen vacancy-related defects. According to the parallel conductance method, both the interface and border traps were observed for the sample with Al₂O₃. However, the border traps were not observed with including an HfO₂ layer. The lowest interface trap density and the reverse leakage current were obtained for the sample with an HfO₂/Al₂O₃ bilayer. Analysis of x-ray photoelectron spectroscopy spectra obtained from the HfO₂ layers showed the formation of Hf-Al-O bonding for the sample with HfO₂ while such formation was not observed for the sample with HfO₂/Al₂O₃. These results indicate the superior interfacial quality of AlN/GaN heterostructures with an HfO₂/Al₂O₃ bilayer.