Quarter micron low noise GaAs FET's

Studies directed towards the development of the quarter-micron-gate FET were initiated at a time when the production of half-micron-gate GaAs MESFET's had become possible. The present investigation is concerned with some optically defined 0.25 micrometer gate FET's with a performance which is superior to that provided by state-of-the-art E-beam devices. The devices were fabricated on vapor phase epitaxial material using the hydride process. The sulfur doped active layers were grown in-situ over buffer layers on semiinsulating GaAs substrates. An abrupt active/buffer interface leads to excellent device transconductance at low noise bias. Chemical etching was used to isolate the mesas. Source and drain ohmic contacts were alloyed AuGe/Ni/Au. The technique employed to create the gate involved a combination of electron beam generated masks with contact printing lithography and angle evaporated metal.