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 350mS/mm at 300K and 380mS/mm at 77K, maximum drain current of 350mA/mm at 300K and 400mA/mm at 77K for 0.8/spl mu/m gate lengths) and low gate leakage. A drift mobility of 20,000 cm/sup 2/V/sup -1s-1/ is measured at 77K for the implanted GaAs SISFETs while 150,000 cm/sup 2/V/sup -1s-1/ is measured for the as-grown heterostructures. Small circuits, fabricated with these enhance-deplete GaAs SISFETs, are de- scribed.