Improvement of DC and RF characteristics of AlGaN/GaN high electron mobility transistors by thermally annealed Ni/Pt/Au schottky gate

A thermally annealed Ni/Pt/Au metal structure was employed as the gate contacts of AlGaN/GaN high electron mobility transistors (HEMTs), and their DC and RF performances were investigated. This gate structure markedly improved the Schottky characteristics such as the Schottky barrier height and leakage current. Regarding the DC characteristics, the maximum drain current and off-state breakdown voltage were increased from 0.78 A/mm (V_g = 1 V) to 0.90 A/mm (V_g = 3 V) due to the improved applicability of the gate voltage and from 108V to 178V, respectively, by annealing the gate metals. In addition, a reduction of the transconductance was not observed. Furthermore, even after the deposition of SiN_x passivation film, the off-state breakdown voltage remained at a relatively high value of 120V. Regarding the RF characteristics, the cut-off frequency and maximum oscillation frequency were also improved from 10.3 GHz to 13.5 GHz and from 27.5 GHz to 35.1 GHz, respectively, by annealing the gate metals whose gate length was 1 μm.