Annealing kinetics of vacancy-related defects in low-dose MeV self-ion-implanted<i>n</i>-type silicon

Abstract

Silicon samples of n-type have been implanted at room temperature with 5.6-MeV ${}^{28}\mathrm{Si}$ ions to a dose of $2\ifmmode\times\else\texttimes\fi{}{10}^{8}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ and then annealed at temperatures from 100 to 380 \ifmmode^\circ\else\textdegree\fi{}C. Both isothermal and isochronal treatments were performed and the annealing kinetics of the prominent divacancy ${(V}_{2})$ and vacancy-oxygen (VO) centers were studied in detail using deep-level transient spectroscopy. The decrease of ${V}_{2}$ centers exhibits first-order kinetics in both Czochralski-grown (CZ) and float-zone (FZ) samples, and the data provide strong evidence for a process involving migration of ${V}_{2}$ and subsequent annihilation at trapping centers. The migration energy extracted for ${V}_{2}$ is \ensuremath{\sim}1.3 eV and from the shape of the concentration versus depth profiles, an effective diffusion length \ensuremath{\leqslant}0.1 \ensuremath{\mu}m is obtained. The VO center displays a more complex annealing behavior where interaction with mobile hydrogen (H) plays a key role through the formation of VOH and ${\mathrm{VOH}}_{2}$ centers. Another contribution is migration of VO and trapping by interstitial oxygen atoms in the silicon lattice, giving rise to vacancy-dioxygen pairs. An activation energy of \ensuremath{\sim}1.8 eV is deduced for the migration of VO, in close resemblance with results from previous studies using electron-irradiated samples. A model for the annealing of VO, involving only three reactions, is put forward and shown to yield a close quantitative agreement with the experimental data for both CZ and FZ samples over the whole temperature range studied.