SIMPLIFIED SIMULATIONS OF GAAS-MESFETS WITH SEMIINSULATING SUBSTRATE COMPENSATED BY DEEP LEVELS

Current-voltage characteristics of GaAs metal-semiconductor field effect transistors (MESFET's) (with p-buffer layers) on semi-insulating substrates compensated by deep levels are simulated by two-carrier and one-carrier models. For a thicker p-buffer layer or for higher acceptor density in the substrate, the drain current becomes lower because the substrate current is reduced. The one-carrier model also gives reasonable results for a case with a hole-trap substrate. Small-signal parameters of GaAs MESFET's on various types of substrates are also simulated. It is found that for a thicker p-buffer layer or for higher acceptor densities in the semi-insulating substrates, the substrate current is reduced, and both transconductance and cutoff frequency become higher. It is concluded that to utilize high-speed and high-frequency performance of GaAs MESFET's, acceptor densities in the substrate should be made high.