Observation and analysis of negative resistance in the forward I-V characteristics of dielectrically isolated high-voltage gated diode switches

A current-controlled negative resistance in the forward current-voltage characteristics is observed on some dielectrically isolated gated diode switches (GDS). Defect etching of the devices that exhibited negative resistance showed a high density of defects compared to devices that did not. The high density of defects in the cathode implied a possible resistive shunting of the n⁺-p junction. To verify this, special test structures were used with an external resistor shunting of the n⁺-p cathode to simulate the effects of defects. The characteristics of the GDS with the externally connected resistor shunt exhibited negative resistance similar to that with high defect density devices. When the external shunt was removed the characteristics did not show any negative resistance. Thus we infer that the cause of the negative resistance in our original samples is the resistive shunting effect of the defects in the cathode. A simple physical model for the negative resistance is presented and corroborated with our experimental observations.