Photoconductivity Studies of Radiation-Induced Defects in Silicon

Abstract

The annealing behavior and the uniaxial-stress responses of the radiation-induced defect causing the ${E}_{c}\ensuremath{-}0.75$-, ${E}_{c}\ensuremath{-}0.54$-, ${E}_{c}\ensuremath{-}0.42$-, and ${E}_{c}\ensuremath{-}0.18$-eV photoconductivity energy levels in $n$-type silicon were studied after 1.5-MeV electron and $^{60}\mathrm{Co}$ $\ensuremath{\gamma}$-ray irradiation at 300 \ifmmode^\circ\else\textdegree\fi{}K. The results suggest that the ${E}_{c}\ensuremath{-}0.75$-eV level arises from the electronic transition of the neutral charge state of the divacancy to the conduction band. This level also occurs in heavily irradiated $p$-type silicon when the Fermi level is too high to observe the divacancy-associated 0.32-eV photoconductivity band. The ${E}_{c}\ensuremath{-}0.75$-eV level is found to be correlated with the 0.32-eV band, indicating that they are due to two different charge states of the same defect. The ${E}_{c}\ensuremath{-}0.18$-eV level arises from the $A$-center defect which exhibits only one kind of stress response, i.e., the atomic redistribution among the allowable orientations. No electronic response was observed for the $A$ center in our photoconductivity measurements. Our data fit very well with the $A$-center model derived from electron-paramagnetic-resonance studies. The ${E}_{c}\ensuremath{-}0.42$-eV level was quite complicated. Besides the radiation-induced divacancy defect located near this level, we present evidence that some additional trap center inherent as an in-grown defect in the sample also gives rise to this level. The ${E}_{c}\ensuremath{-}0.54$-eV level anneals out around 150 \ifmmode^\circ\else\textdegree\fi{}C. Whether it really arises from the singly charged state of the divacancy or not is still a question.