ELECTRICAL PROPERTIES OF NEUTRON-IRRADIATED SILICON AT 76 DEGREES K - HALL EFFECT AND ELECTRICAL CONDUCTIVITY

Defects produced in p-type silicon by neutron irradiation have been investigated using electrical conductivity and Hall effect measurements at 76°K. Samples from crucible-grown (1, 10, and 50 ohm-cm) and float-zone (10 ohm-cm) boron-doped silicon were irradiated at 76°K with nearly fission spectrum neutrons and annealed isochronally between 76° and 700°K. The electrical properties of neutron-irradiated p-type silicon exhibit an illumination dependence similar to that observed previously in n-type silicon and attributed to the presence of defect clusters. Therefore, neutron-produced changes in the electrical properties of p-type silicon also are attributed to defect clusters. The sensitivity to illumination was observed for all resistivities and for both crucible and float-zone p-type silicon. The illumination-induced conductivity decays slowly with time at 76°K and influences the thermally produced changes in the electrical properties upon annealing for temperatures up to 150°K. Neutron-produced changes in the electrical properties measured after annealing to 150°K are found to be qualitatively consistent with an insulating void model for cluster-space-charge regions. The best modeling of the experimentally observed changes is for the 50 ohm-cm (large void volume) silicon. The annealing loss of the light sensitive defects occurs in diffuse stages between 150° and 550°K with the largest stage between 150° and 240°K. A major fraction of the hole mobility annealing parallels that for the light sensitive defects and suggests that the mobility change is caused primarily by defect clusters. The most apparent crystal growth dependent annealing is observed between 540° and 620°K where a reverse annealing occurs in the hole removal rate for crucible-grown but not for float-zone silicon. The fractions of the neutron-produced decrease in hole concentration and mobility which remain after 700°K annealing are respectively~ 0.1 and 0.01 for float-zone and ~ 0.25 and 0.1 for crucible-grown 10 ohm-cm silicon. Copyright © 1968 by The Institute of Electrical and Electronics Engineers, Inc.