Gate optimization of AlGaN/GaN HEMTs using WSi, Ir, Pd, and Ni Schottky contacts

High electron mobility transistors (HEMTs) were fabricated from AlGaN/GaN on semi-insulating SiC substrates with WSi, Ir, Pd, and Ni Schottky contacts. The devices had 0.30 /spl mu/m T-gates with a total width of 300 /spl mu/m. Devices with Ir gates had the highest measured Schottky barrier and the best small-signal performance of all gate metal combinations attempted. These devices yielded maximum drain current densities of 1.03 A/mm, peak transconductances of 252 mS/mm, unity current gain cutoff frequencies of 46 GHz, and maximum frequencies of oscillation at 64 GHz. Power measurements of these same devices produced 6.5 W/mm with PAE of 32% at 10 GHz CW when optimizing for power.