Substitution of Impurity Atoms by Self-Interstitials in Thermal Neutron Irradiated Germanium

We have used the recoil energy associated with capture gamma-ray emission subsequent to thermal-neutron absorption to introduce a predetermined concentration of activated 71 Ge self-interstitial atoms into Ge. Some of the 71 Ge may have recombined with vacant lattice sites, but we found that most of the 71 Ge was mobile and migrated to replace a substitutional n- or p-type dopant impurity atom, making it interstitial, if a sufficient concentration of such dopant atoms was available. This model of a replacement is consistent with that proposed by previous investigators for electron-irradiated Si and Ge. Irradiation in another reactor locale with a much lower thermal-to-fast neutron ratio was found to introduce complex defect structures from fast neutron collisions with Ge atoms that trapped a significant fraction of the 71 Ge in an interstitial position.