ENHANCE/DEPLETE GaAs SISFETS.

As-grown (enhancement-mode) and implanted (depletion-mode) GaAs SISFETs are fabricated in selective areas of the same chip with a self-aligned refractory gate process. Both types of devices have comparable characteristics (transconductances of 350 mS/mm at 300 K and 380 mS/mm at 77 K, maximum drain current of 350 mA/mm at 300 K and 400 mA/mm at 77 K for 0. 8- mu m gate lengths) and low gate leakage. A drift mobility of 20,000 cm**2V** minus **1s** minus **1 is measured at 77 K for the implanted GaAs SISFETs while 150,000 cm**2V** minus **1s** minus **1 is measured for the as-grown heterostructures. Small circuits, fabricated with these enhance-deplete GaAs SISFETs, are described.