High f_T AlGa(In)N/GaN HEMTs Grown on Si With a Low Gate Leakage and a High ON/OFF Current Ratio

A 55-nm T-gate high-electron-mobility transistor was fabricated with a quaternary barrier AlGa(In)N/ AlN/GaN heterostructure grown on a highly resistive Si substrate. The device shows a maximum current density of 1.25 A/mm, a peak extrinsic dc transconductance of 420 mS/mm, and the cutoff frequencies fT/fmaxof 145/220 GHz, which gives a record high value of (fT· fmax)1/2 = 178 GHz among the reported GaN-on-Si ratio frequency devices. The Al-rich quaternary barrier featured an incorporation of little indium, which yet significantly improved the crystalline quality, resulting in a record low gate leakage below 10-5A/mm and a high ION/IOFF ratio of 1.78 × 105.