Electrical Studies of Neutron-Irradiatedn-Type Si: Defect Structure and Annealing

Abstract

Hall-effect and electrical-conductivity measurements were used to investigate electrically active defects produced in $n$-type silicon by neutron irradiation. Samples from quartz-crucible, float-zone, Dash, and Lopex silicon were irradiated at 76 and 100°K to study the dependence of defect production and annealing on crystal growth method and irradiation temperature. Defect production by neutron irradiation is found to be relatively independent of both crystal growth method and irradiation temperature, in contrast with the marked dependence observed for electron irradiation. Illumination-sensitive defects are observed following neutron irradiation which are not observed following electron irradiation under the same conditions. The annealing loss of the illumination-sensitive defects closely correlates with the $A$-center growth observed by Whan following neutron irradiation of high-oxygen-content silicon. Whan attributed the $A$-center growth to vacancy liberation from defect clusters. The present correlation suggests that the illumination-sensitive defects are directly associated with vacancy-liberating clusters. Evidence for neutron-produced defect clusters in silicon has recently been obtained in electron-microscope studies by Bertolotti et al. Assuming impurity-dependent trapping of cluster-liberated vacancies, ∼90% of the carrier removal measured at 76°K is due to defect clusters after 120°K annealing; after 300°K annealing, measurements at 76°K indicate that ∼60% of the carrier removal in crucible-grown silicon and ∼50% of the carrier removal in float-zone silicon is due to defect clusters.