Fine structure and electromagnetic radiation in second breakdown

Thermal phenomena have been suggested as the initiating mechanisms for second breakdown in transistors. The experiments described below examine certain electrical and optical effects associated with second breakdown in order to determine if thermal effects can be held primarily responsible. In studying the open-base behavior of several types of devices, it was observed that second breakdown was followed by additional discontinuities at higher current levels, all similar to second breakdown in their electrical behavior. Simultaneously with the appearance of a voltage discontinuity, light was emitted by the device. The light output level generally increased monotonically with increasing collector current except when a voltage discontinuity occurred, at which time a discontinuous increase in the light output level also occurred. The spectral distribution of the emitted light was examined and found to be similar to the distribution from a single junction biased into avalanche. The results of the electrical measurements strongly suggest the existence of a number of interacting sites capable of sustaining second breakdown. The optical measurements indicate that the characteristics of a transistor in second breakdown are not purely thermal in nature, but that a plasma effect may be associated with a device exhibiting an anomalous breakdown.