Formation and origin of the dominating electron trap in irradiatedp-type silicon

Abstract

Deep level transient spectroscopy and minority-carrier transient spectroscopy (MCTS) have been applied to study electron-irradiated and proton-irradiated $p$-type Si samples with boron concentrations in the range of $6\ifmmode\times\else\texttimes\fi{}{10}^{13}\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}{10}^{15}\text{ }{\text{cm}}^{\ensuremath{-}3}$. Both impurity-lean epitaxially grown samples and Czochralski grown samples have been investigated where some of the epitaxial samples were subjected to oxygenation prior to the irradiation in order to controllably vary the oxygen concentration. The MCTS measurements reveal a dominant electron trap at ${E}_{c}\ensuremath{-}0.25\text{ }\text{eV}$, where ${E}_{c}$ is the conduction-band edge, commonly ascribed to a boron-interstitial oxygen-interstitial complex $({\text{B}}_{i}{\text{O}}_{i})$. The amplitude of the level increases linearly with the irradiation dose and it anneals out at $\ensuremath{\sim}175\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ but shows, however, no correlation with the boron concentration. The level is dominant even at doping concentrations in the ${10}^{13}\text{ }{\text{cm}}^{\ensuremath{-}3}$ range and, irrespective of the oxygen concentration, the generation rate decreases by almost 50% as the boron concentration increases by a factor of $\ensuremath{\sim}30$. Comparison with numerical modeling reveals that these results are not consistent with the commonly accepted model of defect reactions in irradiated $p$-type Si. Different reasons for this discrepancy are discussed, such as an incomplete defect reaction model and alternative identifications of the ${E}_{c}\ensuremath{-}0.25\text{ }\text{eV}$ level.