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: σ_n=2.2×10⁻¹⁷ cm²; σ_p=6×10⁻¹⁵ cm², the latter value being correct only within about a factor of two. The ratio of the cross sections, σ_p/σ_n, 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.