Improving Performance of Al₂O₃/AlN/GaN MIS HEMTs via In Situ N₂ Plasma Annealing

A novel monocrystalline AlN interfacial layer formation method is proposed to improve the device performance of the fully recessed-gate Al₂O₃/AlN/GaN Metal-Insulator-Semiconductor High Electron Mobility Transistors (MIS-HEMTs), which is achieved by plasma-enhanced atomic layer deposition (PEALD) and in situ N₂ plasma annealing (NPA). Compared with the traditional RTA method, the NPA process not only avoids the device damage caused by high temperatures but also obtains a high-quality AlN monocrystalline film that avoids natural oxidation by in situ growth. As a contrast with the conventional PELAD amorphous AlN, C-V results indicated a significantly lower interface density of states (D_it) in a MIS C-V characterization, which could be attributed to the polarization effect induced by the AlN crystal from the X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM) characterizations. The proposed method could reduce the subthreshold swing, and the Al₂O₃/AlN/GaN MIS-HEMTs were significantly enhanced with ~38% lower on-resistance at V_g = 10 V. What is more, in situ NPA provides a more stable threshold voltage (V_th) after a long gate stress time, and ΔV_th is inhibited by about 40 mV under V_g,stress = 10 V for 1000 s, showing great potential for improving Al₂O₃/AlN/GaN MIS-HEMT gate reliability.