Emitter avalanche currents in gated transistors

The creation of interface states and the trapping of charge in the oxide during avalanche breakdown of the emitter-base (e-b) junction of planar transistors was studied. Two types of n-p-n transistors, differing in the amount of boron in the base region, were investigated. The creation of interface states was largest in the transistors with a higher concentration of boron in the base region, probably due to a higher density of avalanche plasma near the Si-SiO2interface. The amount of negative charge trapped in the oxide during breakdown with a positive voltage applied to a field plate above the e-b junction was found to be related to the magnitude of the current through the oxide during breakdown. This current is obviously due to hot electrons injected into the oxide. A fraction of these electrons is trapped with about the same efficiency in both types of transistors.