Electron-Irradiation Effects in Silicon at Liquid-Helium Temperatures Using ac Hopping Conductivity

Changes in ac hopping conductivity with electron irradiation have been measured in n-type, p-type, and high-purity silicon. Irradiations were carried out at both 5.0 and 1.6 ^∘{}K, with measurements made at reference temperatures of 4.2 and 1.3 ^∘{}K, respectively. In the p-type crystals, the changes in ac hopping conductivity depend strongly on the concentration of chemical acceptors, indicating a concentration dependence on impurities in the defect production rate. The production rates at 1.6 ^∘{}K were generally very similar to those for a 5.0 ^∘{}K irradiation. No significant thermal annealing stages below room temperature were observed in any of the crystals. No radiation annealing effects due to a beam of either 0.500-MeV or 0.350-MeV electrons were observed, either at 4.5 or 1.45 ^∘{}K. The possibility of athermal effects leading to interstitial migration is suggested.