The Effects of Neutron Irradiation on Germanium and Silicon

The known effects of neutron irradiation upon majority and minority carrier properties of germanium and silicon are reviewed, and used as a basis to derive a theoretical expression for the dependence of grounded-emitter current gain of a transistor upon accumulated neutron dose. This theoretical expression assumes a Shockley-Read recombination mechanism in the base of the transistor; the crystal defects introduced by bombardment act as recombination sites. A number of germanium and silicon transistors were irradiated at different facilities; the observed changes in transistor parameters are explained in terms of the theory. This explanation enables determination for germanium of certain basic quantities in recombination theory, viz., the position in the forbidden band of the recombination site (Ec-Et=0.23 ev), and the capture cross section of the site for hole and electron capture (σp= 1.0×10-5 cm2, and σn≃4×10-15 cm2).