High performance AlGaN/GaN MISHEMTs using N₂O treated TiO₂ as the gate dielectric

Abstract In this work, TiO 2 thin films deposited by the atomic layer deposition (ALD) method were treated with a special N 2 O plasma surface treatment and used as the gate dielectric for AlGaN/GaN metal insulator semiconductor high electron mobility transistors (MISHEMTs). The N 2 O plasma surface treatment effectively reduces defects in the oxide during low-temperature ALD growth. In addition, it allows oxygen atoms to diffuse into the device cap layer to increase the barrier height and thus reduce the gate leakage current. These TiO 2 films exhibit a dielectric constant of 54.8 and a two-terminal current of 1.96 × 10 −10 A mm −1 in 2 μ m distance. When applied as the gate dielectric, the AlGaN/GaN MISHEMT with a 2 μ m-gate-length shows a high on/off ratio of 2.59 × 10 8 and a low subthreshold slope (SS) of 84 mV dec −1 among all GaN MISHEMTs using TiO 2 as the gate dielectric. This work provides a feasible way to significantly improve the TiO 2 film electrical property for gate dielectrics, and it suggests that the developed TiO 2 dielectric is a promising high- κ gate oxide and a potential passivation layer for GaN-based MISHEMTs, which can be further extended to other transistors.