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

Microwave characterization on 1-micron 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 30 GHz), and circuit parameters, such as small-signal transconductance, input capacitance, and output resistance, and displayed sharper pinchoff effects than those of the MESFET's. The input capacitance 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.