Interfacial gate resistance in Schottky-barrier-gate field-effect transistors

We discuss in depth a previously overlooked component in the gate resistance R_g of Schottky-Barrier-Gate FETs, in particular, 0.1-μm gate-length AlInAs/GaInAs MODFETs. The high-frequency noise and power gain of these FETs depend critically on R_g. This has been the motivation for the development of T-gates that keep the gate finger metallization 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 SBGFETs, there appears to exist a smallest practically achievable normalized interfacial gate resistance r_gi on the order of 10^-7 Ω cm²