Low noise, 17-GHz GaAs FET with ion-implanted channel

CONSIDERABLE SUCCESS has been achieved in the fabrication of low-noise microwave GaAs FETs using high quality epitaxial layers. Ion implantation has been used previously to fabricate the FET channel, but some doubt as to the possibility of obtaining low noise operation has remained. Annealling to activate the implant was accomplished with a silicon dioxide capping layer. Electron concentrations in the implanted layers varied less than 30% from end to end of the boule and across the 8 cm-2 area wafers. Typical mobilities were 4200 cm2/V-sec. Gate geometry is a straight 1 p m by 300 pm stripe divided in four equal fingers by two gate pads. The ohmic contacts were Au-Ge/Ni and the gate was Al. As a result of close control of the contact masking process and the excellent uniformity of the implanted layer, high yield was obtained.