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}_{\text {SD}} ) of 5~\mu \text {m} , width ( {W} ) of {2}\times {50}\,\,\mu \text {m} and gate length ( {L}_{G} ) of 200 nm are fabricated and characterized. The relative position of the gate is varied with constant {L}_{\text {SD}} . The value of saturation drain current ( {I}_{\text {DS},\text {sat}} ) and maximum transconductance ( {g}_{m,\text {max}} ) change from 740 mA/mm and 168 mS/mm for gate to source separation ( {L}_{\text {GS}} ) of 3.8~\mu \text {m} to 1071 mA/mm and 245 mS/mm for {L}_{\text {GS}} = {0.25}\,\,\mu \text {m} , respectively. The corresponding breakdown voltage ( {V}_{\text {br}} ) significantly improves from 65 V (for {L}_{\text {GS}} = {3.8}\,\,\mu \text {m} ) to 189 V (for {L}_{\text {GS}} = {0.25}\,\,\mu \text {m} ). The unity current gain frequency ( {f}_{T} ) is observed to remain constant at 55 GHz 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.