On the Neutron Bombardment Reduction of Transistor Current Gain

Abstract

Detailed measurements of the fast-neutron and gamma-ray bombardment behavior of germanium-alloy-transistor current-gain have been obtained concurrent with exposure. These data indicate that previously reported analyses, which lead to a linear dependence of common-base current-gain on fast neutron exposure, yield a good approximation for the npn device, but are not of general validity for the pnp germanium transistor. The extent of departure from the linear approximation depends on the width and conductivity of the base-region and can be appreciable in many cases of practical interest. For the pnp germanium transistor it is necessary to take additional account of both changes during bombardment of the minority-carrier recombination rate at bombardment introduced and initially present recombination centers and changes in the width of the collector junction depletion layer. Observed bombardment curves are in good agreement with an analysis which includes these effects. From initial slopes of the current-gain bombardment curves, values of the product of fast-neutron-exposure times minority-carrier-lifetime at bombardment introduced recombination centers are 9.7×107 for 2.7 ohm-cm p-type and 14.2×107, 6.0×107, and 1.3×107, for 3.6 ohm-cm, 1.2 ohm-cm, and 0.2 ohm-cm n-type germanium, respectively, in units of sec-neutrons/cm2.