Interfacial effects related to backgating in ion-implanted GaAs MESFET´s

Deep trap levels in Si-implanted GaAs FET\´s have been observed, using backgating and optical excitation. Transconductance decays, as deduced from drain-current transients, were generated either by applying a voltage pulse train to the semi-insulating substrate, or with an infrared photon pulse to the FET. These decays were analyzed for their trap emission rate parameters, and a "signature" obtained for the deep levels so activated. Additionally, the spectral dependence of the (photo-FET) transconductance was measured, as a cross check on the trap energies. A 0.81-eV electron trap prominent in backgating experiments was readily shown to match the EL2 native donor signature. Also found from the backgating work were the EB3 and EB4 electron traps, related to lattice damage. These and other effects detected could result from part of the so-called "U-band" of implantation defects that resists thermal annealing. It is likely that these defects congregate near the FET channel-substrate interface, and the measurements are most sensitive to traps in that interfacial region.