A Normally-Off Tungsten-Gated p-AlGaN/u-GaN Composite-Channel p-MESFET With Negligible Hysteresis and a High $\textit{I}_{\text{ON}}$/$\textit{I}_{\text{OFF}}$ Ratio

In this work, an energy band-modulated self-aligned p-AlGaN/u-GaN MESFET with a tungsten (W) gate is demonstrated. A high $\textit{I}_{\text{ON}}$ / $\textit{I}_{\text{OFF}}$ of 2 $\times$ 10 $^{\text{7}}$ , a low subthreshold swing (SS) of 90 mV/dec, and an enhancement-mode threshold voltage ( $\textit{V}_{\text{TH}})$ of $-$ 0.3 V are obtained. Benefiting from the TMAH-treated etching surface and the post gate annealing-treated Schottky interface, an extremely low trap state density of 2.8–4.8 $\times$ 10 $^{\text{11}}$ cm $^{-\text{2}}\cdot$ eV $^{-\text{1}}$ was confirmed by the conductance method. The dual-sweep transfer I – V curves show negligible hysteresis and coincide well even after a harsh long-term OFF-state stress. In addition, the breakdown voltage of the fabricated E-mode p-AlGaN/u-GaN composite-channel MESFET with a gate-to-drain length ( $\textit{L}_{\text{GD}})$ of 4 $\mu $ m reaches $-$ 365 V. The breakdown field reaches approximately 0.9 MV/cm, and the differential ON-resistance is 2.8 k $\Omega\cdot$ mm.