Millimeter-wave ion-implanted graded In/sub x/Ga/sub 1-x/As MESFETs grown by MOCVD

The authors present the fabrication and characterization of ion-implanted graded In/sub x/Ga/sub 1-x/As/GaAs MESFETs. The In/sub x/Ga/sub 1-x/As layers are grown on GaAs substrates by MOCVD (metal-organic chemical vapor deposition) with InAs concentration graded from 15% at the substrate to 0% at the surface. 0.5- mu m gate MESFETs are fabricated on these wafers using silicon ion implantation. In addition to improved Schottky contact, the graded In/sub x/Ga/sub 1-x/As MESFET achieves maximum extrinsic transconductance of 460 mS/mm and a current-gain cutoff frequency f/sub t/ of 61 GHz, which is the highest ever reported for a 0.5- mu m gate MESFET. In comparison, In/sub 0.1/Ga/sub 0.9/As MESFETs fabricated with the same processing technique show an f/sub t/ of 55 GHz. >