Gate Charge Collection and Induced Drain Current in GaAs FETs

Focused electron-beam pulses have been used to study and compare collection of ionization generated charge by the gate and induced drain current in GaAs field-effect transitors. Results indicate that hole collection by the gate occurs principally by diffusion, and that built-in fields at the channel-substrate junction inhibit this collection except at the device edges where the gate directly contacts the semi-insulating substrate. At sufficiently high excitation levels the induced drain current is dominated by photoconduction through the substrate from source to drain, and is enhanced by inherent photoconductive gain. The large magnitude of the drain current response relative to the gate collection suggests that it is an important effect for single-particle events in GaAs devices.