NUMERICAL-SIMULATION OF GAAS-MESFETS ON THE SEMI-INSULATING SUBSTRATE COMPENSATED BY DEEP TRAPS

It is found that higher acceptor density in the substrate results in lower device current due to the formation of a space-charge layer at the channel-substrate interface. The drain currents increase continuously with the drain voltage because electrons are injected to fill the traps in the substrate and a current path through the substrate is formed. This substrate current becomes significant for shorter gate-length MESFETs on a substrate with lower acceptor and trap densities. It is suggested that, to minimize short-channel effects in GaAs MESFETs, the acceptor density as well as the trap density in the semi-insulating substrate must be high.