Analysis of the Effect of Nuclear Radiation on Transistors

Abstract

The behavior of germanium transistors in nuclear radiation fields is predicted by combining transistor theory and the experimentally observed changes in irradiated semiconductors. It is shown that the decay of minority carrier lifetime τ in the base region usually controls the useful life of a transistor in a radiation field. Radiation induced changes of the conductivity place an ultimate limit on transistor life, but these changes occur at a much slower rate than those in τ. The analysis predicts the following: (a) αcb−1 should be a linear function of bombardment time in a constant flux field; (b) p-n-p units should decay faster than n-p-n units; (c) for a given resistivity type and structure the decay rate is proportional to the square of the transistor base width which in turn, is inversely proportional to the cutoff frequency of the amplification factor. Thus, high-frequency units with their thin base regions decay more slowly than low-frequency units. The predictions of the theory are compared with experimental observations on the behavior of irradiated transistors, and the agreement is found to be reasonably good.