Analysis of transistor ICBOexcess currents by gamma irradiation

Excess ICBOcurrents 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.