Monoenergetic Neutron Irradiation of Germanium

Abstract

A study has been made on 14-Mev neutron-irradiated germanium, using lifetime, Hall, and resistivity measurements to determine the nature of the radiation-induced defects and to compare the damage with that produced by neutrons from a fission spectrum. The electron removal rate in high-resistivity, n-type material is ∼8/cm−3 per incident neutron/cm2, measured at 77°K. Lifetime measurements have been made on n- and p-type material. On the basis of simple recombination theory, assuming no variation of capture probabilities with temperature, the results for n-type material indicate that a recombination level is located 0.32 ev above the valence band near the center of the energy gap. Assuming an introduction rate of recombination centers equal to one-half the electron removal rate in n-type material, the following values of recombination capture cross sections are obtained: σn=2.2×10−17 cm2; σp=6×10−15 cm2, the latter value being correct only within about a factor of two. The ratio of the cross sections, σp/σn, which is independent of the method of determining the number of recombination centers, is ∼300, indicating that the recombination centers are negatively charged. The lifetime measurements for p-type germanium are not so readily analyzed. Possible explanations for observed behavior are discussed.