Characteristics of two-stage Γ-gate on AlGaAs/InGaAs/AlGaAs DH-HEMTs by using AlGaAs/InGaP etching-stop layers

Al0.22Ga0.78As/In0.18Ga0.82As/Al0.22Ga0.78As double heterojunction high electron mobility transistors (DH-HEMTs) with gate structures of traditional planar gate (PG), one-stage gamma-gate (1S Gamma G) and two-stage gamma-gate (2S Gamma G) formed by using the Al0.22Ga0.78As/In0.49Ga0.51P etch-stop layers (ESL) are simulated and presented in this work. Based on this proposed ESL structure design, the fabrication and implementation of studied DH-HEMT device with 1S Gamma G and 2S Gamma G could be expected. Both Gamma G-stnicture devices show the better electric field property compared to PG-device. Simulated results reveal that there are no significant differences in common-source voltage-current characteristics among all studied devices. The obtained drain current density and transconductance of all studied devices are about 220 mAmm(-1) and 265 mSmm(-1). However, the current stability of Gamma G-devices with larger bias operation would be improved due to its edge-effect of Gamma G extended-region. In addition, the electric field intensity under the gate-footprint is effectively reduced by both studied Gamma G structures. The electric field peak value of PG-device is 498 kV cm(-1), and it would be reduced down to about 210 kVcm(-1) and 178 kVcm(-1) for 1S Gamma G- and 2S Gamma G-device, respectively. On the other hand, some frequency property dropping is observed from studied device with 1S Gamma G or 2S Gamma G due to the side-edge extension of Gamma G-device would create the additional parasitic capacitance. The obtained cut-off frequencies are 15 GHz, 10.5 GHz and 10 GHz for PG-, 1S Gamma G- and 2S Gamma G-device (at V-GS=+5 V and V-GS=-0.75 V), respectively.