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 g
mo
, C
gs
, and R
ds
displayed sharper pinchoff effects than those of the MESFET's. C
gs
in 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.