Millimeter-Wave Ion-Implanted Graded Inx Ga1-xAs MESFET’s Grown by MOCVD

We present the fabrication and characterization of ion- implanted graded InxGa1-xAs/GaAs MESFET’s. The InxGa1-xAs layers are grown on GaAs substrates by MOCVD with InAs concentration graded from 15 percent at the substrate to 0 percent at the surface. 0.5-µm gate MESFET’s are fabricated on these wafers using silicon ion implantation. In addition to improved Schottky contact, the graded InxGa1-xAs MESFET achieves a maximum extrinsic transconductance of 460 mS/mm and a current-gain cutoff frequency ft of 61 GHz, which is the highest ever reported for a 0.5-µm gate MESFET. In comparison, In0.1Ga0.9As MESFET’s fabricated with the same processing technique show an ft of 55 GHz.