AlGaN/GaN Metal-Insulator-Semiconductor High Electron-Mobility Transistor Using a NbAlO/Al₂O₃ Laminated Dielectric by Atomic Layer Deposition

We investigate the characteristics of AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with a NbAlO/Al₂O₃ lamination dielectric deposited by atomic layer deposition (ALD) as the gate insulator. A large gate voltage swing (GVS) of 3.96 V and a high breakdown voltage of −150 V for the MIS-HEMT were obtained. We present the gate leakage current mechanisms and analyze the reason for the reduction of the leakage current. Compared with traditional HEMTs, the maximum drain current is improved to 960 mA/mm, indicating that NbAlO layers could reduce the surface-related depletion of the channel layer and increase the sheet carrier concentration. In addition, the maximum oscillation frequency of 38.8 GHz shows that the NbAlO high-k dielectric can be considered as a potential gate oxide comparable with other dielectric insulators.