Interfacial gate resistance in Schottky-Barrier-Gate field-effect transistors

We discuss in depth a previously overlooked component in the gate resistance Rg of Schottky-Barrier-Gate FET's, in particular, 0.1-μm gate-length AlInAs/GaInAs MODFET's. The high-frequency noise and power gain of these FET's depend critically on Rg. This has been the motivation for the development of T-gates that keep the gate finger metallization resistance Rga (proportional to the gate width Wg) low, even for very short gate length Lg. Rga 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' Rg is instead caused by a component Rgi that scales inversely with Wg. We interpret Rgi as a metal-semiconductor interfacial gate resistance. The dominance of Rgi 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 rgi on the order of 10-7 Ωcm2.