Improved DC and RF Performance of Novel MIS p-GaN-Gated HEMTs by Gate-All-Around Structure

In this study, we report a novel structure of enhancement-mode metal-insulator-semiconductor high electron mobility transistor (E-mode MIS HEMT) with p-GaN gate by gate-all-around technology. The gate-all-around structure is fabricated by depositing an insulator and gate to surround the p-GaN mesa. The p-GaN length is smaller than the gate length, which would easily turn on the two dimensional electron gas (2DEG) of channel and result in a higher drain current and thus improve the device performance. The gate-all-around p-GaN MIS HEMT has better gate control, better transconductance, and lower gate leakage current. The device exhibits a threshold voltage (Vth) of 1.5 V, a maximum transconductance(Gm.max) of 101 mS/mm, and a drain saturation current density (JDS,max) of 412 mA/mm at a gate bias (Vg) of 5 V. The most important achievement is that the gate leakage current at Vg= 5 V is only 10-8 mA/mm. Moreover, the ratio of drain current density to gate leakage current density (JDS/JGS) is 108 at Vg= 5 V. Finally, the cutoff frequency (ft) and maximum oscillation frequency (fmax) of microwave performance for this gate-all-around device with a 1 μm gate length are 6.0 and 9.8 GHz, respectively.