Kink effect related to the self-side-gating effect in GaAs MESFET´s

A kink effect, an abrupt increase in drain current at high drain voltages, was observed in GaAs MESFET´s with an Al_0.2Ga_0.8As/GaAs heterostructure buffer layer. In these MESFET´s, impact ionization occurs at the drain side along the channel current path at high drain voltages. On the other hand, a side-gating effect occurs when a negative voltage applied to the gate pad of the MESFET (self-side-gating effect). From measurements of the substrate potential, we conclude that hole accumulation generated by the impact ionization at the channel-side GaAs/Al_0.2Ga_0.8 As interface cancels the drain current reduction that arises from the self-side-gating effect. This gives rise to the kink effect we observe