CHARGE-ENHANCEMENT MECHANISMS OF GAAS FIELD-EFFECT TRANSISTORS - EXPERIMENT AND SIMULATION

The charge-collection processes of GaAs field-effect transistors are i nvestigated as a function of the incident laser pulse energy via time- resolved charge-collection measurements and by two-dimensional compute r simulation. The measurements and simulations reveal a feature that p ersists on a time scale of 100 ps, the amplitude of which varies stron gly with the injected carrier density (pulse energy). The appearance o f this feature is associated with a barrier lowering effect at the sou rce/substrate junction, coupled with the drift-assisted transport of e lectrons through the substrate to the drain contact. This behavior is similar, but not identical to bipolar-gain models that have been sugge sted previously. We introduce the concept of ion-track segments and il lustrate their utility in interrogating the complex mechanisms of char ge collection and enhancement in GaAs FETs.