Impact of Gate Metal on the Performance of p-GaN/AlGaN/GaN High Electron Mobility Transistors

Abstract — For conventional GaN-based high electron mobility transistors (HEMTs), the work function of gate metal is critical to electrical parameters, such as OFF-state leakage current, forward operating current, and threshold voltage. A high work function is thus required to maintain Schottky gate contact. In this letter, an enhancement-mode HEMT composed of p-type GaN/AlGaN/GaN was fabricated. Unlike typical HEMTs that the Schottky barrier height is determined by the energy difference between gate metal work function and semiconductor (AlGaN, or GaN) conduction band, the insertion of the p-GaN relieves the constraint of gate metal. In addition, the gate Schottky barrier now correlates to the valence band of the semiconductor. Here we compare the HEMT performance of different gate metals—Ni/Au, Ti/Au, and Mo/Ti/Au. The results reveal that a tradeoff between VTH and output drain current. Index Terms — HEMT, enhancement mode, threshold voltage. I