"Second breakdown" in transistors

"Second breakdown" in transistors has been characterized as an abrupt reduction in V
CE
, at a collector current designated by I
M
, when the transistor is swept through its V
CE
vs I
C
characteristics. A critical review of the literature concerning this phenomenon and a more complete description of its characteristics are given. It appears that "second breakdown" is a more fundamental property of the transistor than has previously been thought. Each of the mechanisms thus far considered in the literature, in particular the "pinch-in" effect and p-n-p-n action, has been examined and found inadequate. The apparent dependence of the initiation of the phenomenon on the quantity of energy absorbed, and on the ambient temperature, indicates that it may be related to some thermal mechanism. This points to the importance of examining "second breakdown" in terms of energy dissipated rather than in terms of voltage or current as has been done to date.