Optically induced backgating transients in GaAs FET's

Long-term current transients have been induced with optical pulses in depletion-mode GaAs field-effect transistors (FET's). The millisecond-to-second duration and the bias dependence of the transients are similar to substrate trapping and backgating events initiated by ionizing radiation. A specific region of a FET-the semiconductor region adjacent to the connecting strip between the gate electrode and the gate bonding pad-is particularly sensitive to optical backgating. In this region low-incident optical energies produce a positive current transient; but when the optical intensity exceeds ∼1 mJ/cm², a transient decrease in current is observed. Optical studies promise to be a simple and convenient means of simulating many of the effects of ionizing radiation.