Semiconductor-gated InGaAs/InAlAs heterostructure transistors (SISFET's)

We have successfully fabricated FET's with In0.53Ga0.47As channels, lattice-matched In0.52Al0.48As gate barriers, and n+ In0.53- Ga0.47As gates. For a barrier thickness of 600 Å and a gate length of 1.7 µm, the maximum transconductance is 250 mS/mm at T = 300 K. From gate capacitance measurements, the cutoff frequency is inferred to be ft= 15 GHz for this gate length. Self-aligned source and drain implants have been used to permit nonalloyed ohmic contacts with a characteristic resistance of 0.1 Ω.mm. The transconductance remains above 210 mS/mm for forward gate bias up to +1.0 V, confirming the usefulness of this gate structure for enhancement-mode devices.