Analysis of transistor ICBOexcess currents by gamma irradiation

Excess I
CBO
currents on silicon planar transistors can be due to surface inversion layers over either the base or collector regions of the wafer. For n-p-n transistors, a collector inversion layer would be associated with a negative charge in the protective oxide over the silicon chip. On the other hand, a base inversion would be associated with a positive oxide charge. Since gamma irradiation produces net positive charge in the oxide, a collector inversion layer would tend to be removed by such irradiation. Base inversion layers would tend to be more heavily inverted. Thus, a method for unambiguous rapid identification of the location of the inversion layer is available by use of gamma irradiation.