Fabrication of enhancement-mode AlGaN/GaN high electron mobility transistors using double plasma treatment

•The double plasma process was carried out by two different etching techniques.•Double plasma treated device exhibited a transconductance of 330 mS/mm.•Completed 0.5 μm gate device exhibited a current-gain cutoff frequency of 18 GHz.•The off-state breakdown voltage of 115 V for 0.5 μm gate device was obtained.•Continuous-wave output power density of 4.3 W/mm was obtained at 2.4 GHz.

We report the fabrication and DC and microwave characteristics of 0.5 μm AlGaN/GaN high electron mobility transistors using double plasma treatment process. Silicon nitride layers 700 and 150 Å thick were deposited by plasma-enhanced chemical vapor deposition at 260 °C to protect the device and to define the gate footprint. The double plasma process was carried out by two different etching techniques to obtain enhancement-mode AlGaN/GaN high electron mobility transistors with 0.5 μm gate lengths. The enhancement-mode AlGaN/GaN high electron mobility transistor was prepared in parallel to the depletion-mode AlGaN/GaN high electron mobility transistor device on one wafer. Completed double plasma treated 0.5 μm AlGaN/GaN high electron mobility transistor devices fabricated by dry etching exhibited a peak transconductance, gm, of 330 mS/mm, a breakdown voltage of 115 V, a current-gain cutoff frequency (fT) of 18 GHz, and a maximum oscillation frequency (fmax) of 66 GHz.