Bias dependence of GaAs and InP MESFET parameters

A comparative analysis of the bias dependence of critical RF parameters in GaAs and InP metal-semiconductor field-effect transistors (MESFET´s) led to the following conclusions. 1) The drain-gate feedback capacitance in GaAs MESFET´s is lower than in InP MESFET´s, because of a stronger tendency in GaAs to form stationary Gunn domains at the typical drain bias levels employed. 2) The drain-source output resistance in InP MESFET´s is lower than in GaAs MESFET´s mainly for high drain current units, a fact which is linked to a substrate related softer pinch-off behavior in InP. 3) The current-gain cutoff frequency fT, in the current saturation range of the GaAs MESFET decreases strongly with drain bias as a result of the formation of the stationary Gunn domain. In the InP MESFET, this effect is weaker. At the optimum bias, fT is only 10-20 percent higher in InP MESFET´s than in GaAs ones.