A Normally-Off Tungsten-Gated p-AlGaN/u-GaN Composite-Channel p-MESFET With Negligible Hysteresis and a High ION/IOFF Ratio

In this work, an energy band-modulated self-aligned p-AlGaN/u-GaN MESFET with a tungsten (W) gate is demonstrated. A high
${I}_{\text {ON}}$
/
${I}_{\text {OFF}}$
of
$2\times 10^{{7}}$
, a low subthreshold swing (SS) of 90 mV/dec, and an enhancement-mode threshold voltage (
${V}_{\text {TH}}$
) 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–
$4.8\times 10^{{11}}$
cm
$^{-{2}}\cdot $
eV
$^{-{1}}$
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 (
${L}_{\text {GD}}$
) 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.