Impact of Relative Gate Position on DC and RF Characteristics of High Performance AlGaN/GaN HEMTs

We have investigated the impact of relative gate position between source and drain on the DC and RF characteristics for AlGaN/GaN high electron mobility transistors. Devices with fixed source drain separation (L
_SD
) of 5 μm, width (W) of 2×50 μm and gate length (L
_G
) of 200 nm are fabricated and characterized. The relative position of the gate is varied with constant L
_SD
. The value of saturation drain current (I
_DS,sat
) and maximum transconductance (g
_m,max
) change from 740 mA/mm and 168 mS/mm for gate to source separation (LGS) of 3.8 μm to 1071 mA/mm and 245 mS/mm for L
_GS
= 0.25 μm, respectively. The corresponding breakdown voltage (V
_br
) significantly improves from 65 V (for L
_GS
= 3.8 μm) to 189 V (for L
_GS
= 0.25 μm). The unity current gain frequency (f
_T
) is observed to remain constant at 55GHz for all positions of the gate. However, output power density is found to increase from 3.8 to 5.1 W/mm for the same relative change in the gate position.