INTERFACIAL GATE RESISTANCE IN SCHOTTKY-BARRIER-GATE FIELD-EFFECT TRANSISTORS

We discuss in depth a previously overlooked component in the gate resi stance R-g of Schottky-Barrier-Gate FET's, in particular, 0.1-mu m gat e-length AlInAs/GaInAs MODFET's. The high-frequency noise and power ga in of these FET's depend critically on R-g, This has been the motivati on for the development of T-gates that keep the gate finger metallizat ion resistance R-ga (proportional to the gate width W-g) low, even for very short gate length L-g. R-ga increases with frequency due to the skin effect, but our three-dimensional (3-D) numerical modeling shows conclusively that this effect is negligible. We show that the always ' 'larger-than-expected'' R-g is instead caused by a component R-gi that scales inversely with W-g. We interpret R-gi as a metal-semiconductor interfacial gate resistance. The dominance of R-gi profoundly affects device optimization and model scaling. For GaAs and InP-based SBGFET' s, there appears to exist a smallest practically achievable normalized interfacial gate resistance r(gi) on the order of 10(-7) Omega cm(2).