Nonlinear high frequency response of GaAs metal-semiconductor field effect transistors.

Calculations show that phase nonlinearity in 1micron gate length power GaAs MESFET's can be accounted for by the variation of gate-channel capacitance with gate bias voltage. Buried-layer GaAs MESFET's having constant gate-channel capacitance have been fabricated and their high-frequency linearity measured. The devices display dramatic reductions of phase nonlinearity to 0.15degrees/watt output power at 6 GHz for powers below saturation in 8mm gate-width devices confirming that nonlinear capacitance causes nonlinearity observed in conventional GaAs MESFET's. Channel transit time, estimated at 3-6 psec, is not significant as a cause of nonlinearity and varies less than 100 femtoseconds with signal level.