STRONG NEGATIVE TRANSCONDUCTANCE IN IN-PLANE-GATE TRANSISTORS WRITTENBY FOCUSED-ION-BEAM IMPLANTATION

A strong negative transconductance is investigated in in-plane-gate tr ansistors written by focused-ion-beam implantation in the two-dimensio nal electron gas in modulation-doped AlGaAs/GaAs heterostructures. Thi s occurs in a configuration where two in-plane gates G1 and G2 used to control the current through a channel lying between them are biased w ith different voltages V(g1), and V(g2). When the voltage V(g2)<0 is h eld constant, the current through the channel can be reduced to zero b y increasing V(g1) beyond a critical value. In an earlier study this e ffect was attributed to velocity modulation. It is found, however, tha t in this regime V(g1) causes a very small current I(g2) to flow acros s gate G2. It is observed that changes in I(d) are correlated to chang es in I(g2) and thus conclude that I(g2) is responsible for the strong negative transconductance.