THE INFLUENCE OF SUBSTRATE COMPENSATION ON INTER-ELECTRODE LEAKAGE AND BACK-GATING IN GAAS-MESFETS

Substrate leakage between electrodes and back-gating are two major non-idealities which affect device and circuit performance in GaAs integrated circuits fabricated on semi-insulating substrates. Simple analytical models and simulation results are presented to elucidate the roles of substrate compensation type, carrier densities and trap parameters in the manifestation of these effects. Chrome-doped substrates exhibit long-range negative-bias back-gating because the bias is supported across the channel-substrate junction. Undoped LEC substrates are insensitive to long-range back-gating in either direction unless holes are introduced (e.g. by radiation) or fast transients are present. Above the onset voltage for TFL conduction, both substrates exhibit strong back-gating. While p-wells tied to a voltage source reduce back-gating, floating p-wells or wells shallower than the device n+ implants can significantly worsen back-gating.