Correlation between surface-state density and impact ionization phenomena in GaAs MESFET's

GaAs MESFET's passivated with PECVD SiN show a lower surface-state density in comparison with SiO passivated devices, as deduced from g/sub m/(f) dispersion curves. Lower carrier multiplication due to impact ionization phenomena in the active channel and consequently a higher breakdown voltage are observed in SiO passivated samples. These effects are attributed to a lower peak electric field near the drain edge of the gate, deriving from an accumulation of negative surface charge.<
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