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.