Microwave characterization of (Al,Ga)As/GaAs modulation-doped FET's: Bias dependence of small-signal parameters

Microwave characterization on 1-µm gate (Al, Ga)As/GaAs modulation-doped field-effect transistors (MODFET's) was done using a network analyzer. Equivalent circuit parameters were computed and compared to those of GaAs MESFET's with an identical geometry. The MODFET's had higher current-gain and power-gain cutoff frequencies (18 and 38 GHz versus 14 and 30GHz) and the circuit parameters gmo, Cgs, and Rdsdisplayed sharper pinchoff effects than those of the MESFET's. Cgsin the MODFET displayed a gate bias dependence due to widening of the potential well in the channel. This information should prove valuable in the development of MODFET computer models for circuit simulation.