In this letter, an enhancement-mode (E-mode) GaN p-channel field-effect transistor (p-FET) with a high current density of ?4.9 mA/mm based on a O₃-Al₂O₃/HfO₂ (5/15 nm) stacked gate dielectric was demonstrated on a p⁺⁺-GaN/p-GaN/AlN/AlGaN/AlN/GaN/Si heterostructure. Attributed to the p⁺⁺-GaN capping layer, a good linear ohmic I?V characteristic featuring a low-contact resistivity (ρ_c) of 1.34 × 10^?4 Ω·cm² was obtained. High gate leakage associated with the HfO₂ high-k gate dielectric was effectively blocked by the 5-nm O₃-Al₂O₃ insertion layer grown by atomic layer deposition, contributing to a high I_ON/I_OFF ratio of 6 × 10⁶ and a remarkably reduced subthreshold swing (SS) in the fabricated p-FETs. The proposed structure is compelling for energy-efficient GaN complementary logic (CL) circuits.

In this work, the GaN p-MISFET with LPCVD-SiN_x is studied as a gate dielectric to improve device performance. By changing the Si/N stoichiometry of SiN_x, it is found that the channel hole mobility can be effectively enhanced with Si-rich SiN_x gate dielectric, which leads to a respectably improved drive current of GaN p-FET. The record high channel mobility of 19.4 cm²/(V?s) was achieved in the device featuring an Enhancement-mode channel. Benefiting from the significantly improved channel mobility, the fabricated E-mode GaN p-MISFET is capable of delivering a decent-high current of 1.6 mA/mm, while simultaneously featuring a negative threshold-voltage (V_TH) of –2.3 V (defining at a stringent criteria of 10 μA/mm). The device also exhibits a well pinch-off at 0 V with low leakage current of 1 nA/mm. This suggests that a decent E-mode operation of the fabricated p-FET is obtained. In addition, the V_TH shows excellent stability, while the threshold-voltage hysteresis ΔV_TH is as small as 0.1 V for a gate voltage swing up to –10 V, which is among the best results reported in the literature. The results indicate that optimizing the Si/N stoichiometry of LPCVD-SiN_x is a promising approach to improve the device performance of GaN p-MISFET.

Power electronic devices are of great importance in modern society. After decades of development, Si power devices have approached their material limits with only incremental improvements and large conversion losses. As the demand for electronic components with high efficiency dramatically increasing, new materials are needed for power device fabrication. Beta-phase gallium oxide, an ultra-wide bandgap semiconductor, has been considered as a promising candidate, and various β-Ga₂O₃ power devices with high breakdown voltages have been demonstrated. However, the realization of enhancement-mode (E-mode) β-Ga₂O₃ field-effect transistors (FETs) is still challenging, which is a critical problem for a myriad of power electronic applications. Recently, researchers have made some progress on E-mode β-Ga₂O₃ FETs via various methods, and several novel structures have been fabricated. This article gives a review of the material growth, devices and properties of these E-mode β-Ga₂O₃ FETs. The key challenges and future directions in E-mode β-Ga₂O₃ FETs are also discussed.