GENERATION MECHANISM OF GATE LEAKAGE CURRENT DUE TO REVERSE-VOLTAGE STRESS IN I-ALGAAS N-GAAS HIGFETS/

Device degradation characterized as an increase in the gate leakage cu rrent due to continuous reverse-voltage stress was investigated for a 0.35-mu m WSi gate i-AlGaAs/n-GaAs doped channel HIGFET (heterostructu re insulated-gate field-effect transistor), The gate leakage current, which was dominated by a hole current generated by impact ionization, was found to increase after the application of a gate-to-drain voltage of -6 V for a certain period, The occurrence of the impact ionization was evidenced by the generation of a substrate current and by the neg ative temperature coefficient of the gate current, The degradation was retarded at an elevated temperature, indicative of hot-carrier-relate d degradation, The degraded device also showed an ohmic-like gate leak age current, Subsequent annealing at temperatures above 300 degrees C significantly restored the current-voltage (I-V) characteristics. From these observations, a degradation model was developed in which hot ho les generated by impact ionization are trapped in the insulator/semico nductor interface, contracting the surface depletion region and thereb y increasing the electric held near the gate-edge. A surface treatment using CF4 plasma was used to suppress the degradation. An FET fabrica ted using this treatment showed a remarkable decrease in degradation.