Abstract:
In this letter, enhancement-mode (E-mode) Al
2O
3/AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) with a gate-length (L
g) of 0.25
μm are fabricated using gate recess and ALD-Al
2O
3 process on a sapphire substrate. The fabricated E-mode MIS-HEMTs exhibit a threshold voltage of +2.2 V and a saturation drain current of 512.3 mA/mm at V
GS=8 V. The interface trap state density (D
it) extracted by frequency/temperature-dependent capacitance-voltage (C-V) measurement between Al
2O
3 and AlGaN decreases from 8.50×10
12 cm
-2eV
-1 at the energy of (
EC-0.35) eV to 9.73×10
11 cm
-2eV
-1 at (
EC-0.65) eV. In addition, the fabricated devices show excellent RF performance which consists of a cut-off frequency (
fT) of 30.5 GHz and a maximum oscillation frequency (
fmax) of 71.5 GHz. Large-signal power measurements at 8 GHz reveal a maximum saturated output power density of 1.7 W/mm with a corresponding PAE of 32.6% in continuous-wave mode. These results showed the gate-recessed E-mode MIS-HEMTs are candidates for X-band applications.