120 - nm -T-shaped-Mo∕Pt∕Au-gate AlGaN∕GaN high electron mobility transistors

We fabricated 120-nm-T-shaped-Mo∕Pt∕Au-gate AlGaN∕GaN high electron mobility transistors (HEMTs) on sapphire substrates. The gate leakage current Igs of the Mo∕Pt∕Au-gate HEMT at a gate-source voltage Vgs of −5V was as much as five orders of magnitude lower than that of the Ni∕Pt∕Au-gate HEMT under the as-deposited condition. The off-state breakdown voltage, defined as the gate-source voltage when the gate-source current is −1mA∕mm, was about −60V for the Mo∕Pt∕Au-gate HEMT. These dc performances are comparable to those of the Ni∕Pt∕Au-gate HEMTs in which the Schottky contacts were improved with rapid thermal annealing at 500°C. The Mo∕Pt∕Au-gate HEMTs also exhibited good rf performance without RTA. The cutoff frequency fT was more than 50GHz and the maximum oscillation frequency fmax was about 100GHz.