MESFETs with nonalloyed ohmic contacts using a graded n/sup +/ (InGa)As cap layer

Results are presented on GaAs MESFET devices with nonalloyed ohmic contacts fabricated using a graded (InGa)As cap layer. Nonalloyed contacts do not require the ohmic alloy step and have much smoother morphology than alloyed metal contacts, permitting more reproducible and accurate gate-level lithography. Specific contact resistances of 1*10/sup -7/ Omega -cm/sup 2/ were measured on FETs that exhibited g/sub m/=210 mS/mm and f/sub t/=23 GHz at 300 K for devices with 0.6- mu m gate lengths.>