A Normally-Off Tungsten-Gated p-AlGaN/u-GaN Composite-Channel p-MESFET With Negligible Hysteresis and a High I ON/I 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 <tex-math notation="LaTeX">ION</tex-math> / <tex-math notation="LaTeX">IOFF</tex-math> of 2 <tex-math notation="LaTeX">×</tex-math> 10 <tex-math notation="LaTeX">⁷</tex-math> , a low subthreshold swing (SS) of 90 mV/dec, and an enhancement-mode threshold voltage ( <tex-math notation="LaTeX">VTH)</tex-math> of <tex-math notation="LaTeX">$-$</tex-math> 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 <tex-math notation="LaTeX">×</tex-math> 10 <tex-math notation="LaTeX">¹¹</tex-math> cm <tex-math notation="LaTeX">⁻²·</tex-math> eV <tex-math notation="LaTeX">⁻¹</tex-math> 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 ( <tex-math notation="LaTeX">LGD)</tex-math> of 4 <tex-math notation="LaTeX">μ</tex-math> m reaches <tex-math notation="LaTeX">$-$</tex-math> 365 V. The breakdown field reaches approximately 0.9 MV/cm, and the differential ON-resistance is 2.8 k <tex-math notation="LaTeX">Ω·</tex-math> mm.