Backgate-induced characteristics of ion-implanted GaAs MESFET's

Three important characteristics of GaAs ion-implanted MESFET's associated with the phenomenon of backgating have been identified and measured. These include a negative backgate capacitance, initiation and/or control of low-frequency oscillations, and enhancement of g-r noise, all related to the deep-level electron traps present in the semi-insulating substrate beneath the implanted layer. Low-frequency oscillations have been observed mostly in devices with high gate-leakage current under conditions involving zero to large negative backgate bias. The frequency of oscillations and the backgate negative-capacitance magnitude have been found to decrease and increase, respectively, with the increase of the negative backgate bias voltage. This implies a decrease in the capture/emission cross section of traps at high fields.