Electrical Studies of Electron-Irradiatedn-Type Si: Impurity and Irradiation-Temperature Dependence

Abstract

Electrical-conductivity and Hall-coefficient measurements have been used to investigate the crystal growth and irradiation-temperature dependence of the introduction and annealing of defects in electron-irradiated $n$-type silicon. Irradiations of 10-\ensuremath{\Omega} cm, phosphorus-doped silicon with 1.7-MeV electrons were performed at controlled temperatures between 75 and 300\ifmmode^\circ\else\textdegree\fi{}K, and isochronal annealing was investigated between 80 and 700\ifmmode^\circ\else\textdegree\fi{}K. Both intrinsic defects and impurity-associated defects are observed. The impurity independence of annealing between 100 and 200\ifmmode^\circ\else\textdegree\fi{}K suggests the annealing of intrinsic defects. The introduction rate for these intrinsic defects is independent of the irradiation temperature between 75 and 100\ifmmode^\circ\else\textdegree\fi{}K. The introduction rates for the impurity-associated defects, however, exhibit an exponential dependence on the reciprocal irradiation temperature between 75 and 100\ifmmode^\circ\else\textdegree\fi{}K consistent with a model based on metastable vancacy-interstitial pairs that predicts a temperature-dependent probability for vacancy-interstitial dissociation during irradiation and subsequent trapping by crystal impurities. For irradiations above 100\ifmmode^\circ\else\textdegree\fi{}K, the introduction rates of impurity-associated defects are relatively independent of the irradiation temperature. Excluding the carrier-removal annealing which is associated with the intrinsic-defect stage, 90% of the annealing in crucible-grown silicon and \ensuremath{\sim}70% of the annealing in float-zone, Dash, and Lopex silicon correlate with the annealing of the divacancy and impurity-associated defects observed in EPR and optical-absorption studies on $n$-type silicon. In crucible-grown silicon, the annealing temperatures of the dominant electrically active, impurity-associated defects correlate with those for the $A$ center and other oxygen-associated defects. Measurements of carrier concentration versus temperature provide additional evidence for the dominance of the $A$ center which has an energy level near ${E}_{c}\ensuremath{-}0.185$ eV, where ${E}_{c}$ is the energy of the conduction-band minimum. A level near ${E}_{c}\ensuremath{-}0.13$ eV also is observed in crucible-grown silicon for the oxygen-associated defects responsible for reverse annealing between 200 and 250\ifmmode^\circ\else\textdegree\fi{}K. In float-zone silicon, the annealing temperatures of the dominant electrically active defects correlate with the $E$-center and divacancy annealing. Lopex silicon is very similar to Dash silicon, and in these materials all the annealing stages of crucible and float-zone silicon are observed.