Current mode second breakdown in epitaxial planar transistors

The phenomena of second breakdown in epitaxial planar transistors has been observed to fall into two distinct categories. The first and most widely discussed occurs in the forward biased, active region of the transistor at collector voltages at or below the collector-emitter sustaining voltage. This type is generally believed to be a thermally induced second breakdown resulting from local regenerative heating, tt is characterized by an abrupt reduction in the collector voltage and an associated time constant of several microseconds to many milliseconds. This type of second breakdown can be observed in all types of transistors. The second type of second breakdown, which will be the subject of this paper, has been observed only in epitaxial transistors, particularly those with relatively thin or high resistivity epitaxial skins. This type of second breakdown occurs only at collector voltages in excess of the collector-emitter sustaining voltages. The collapse of collector voltage is characterized by delay and fall times on the order of a nanosecond. The phenomenon is initiated only when the emitter is injecting.