Formation of a double acceptor center during divacancy annealing in low-doped high-purity oxygenated Si

Deep-level transient spectroscopy studies of electronic defect levels in 7-MeV proton-irradiated n-type float-zone Si with a doping of $(3\mathrm{}–5)\times {10}^{12}{\mathrm{cm}}^{-3}$ and oxygen content of $\sim {10}^{16}–{10}^{17}{\mathrm{cm}}^{-3}$ have been performed. The thermal stability of the irradiation-induced defects has been investigated for temperatures up to 400 °C. It has been found that annealing of the divacancy-related levels, the singly negative, $V_2(0/-),$ and the doubly negative, $V_2(-/=),$ charge states at 220–300 °C results in the formation of a new center with singly negative, $X(0/-),$ and doubly negative, $X(-/=),$ charge states. The new center anneals out at 325–350 °C during isochronal treatment for 15 min. The capture kinetics studies reveal that the electron capture cross section of $X(0/-)$ is larger than that of $V_2(0/-)$ while the capture cross section of $X(-/=)$ is close to that of $V_2(-/=).\mathrm{}$ The transformation of $V_2(0/-)$ and $V_2(-/=)$ into $X(0/-)$ and $X(-/=)$ is very efficient with only a small loss in the peak amplitudes, and the position of the energy levels are close to those of $V_2.$ Hence, it is tempting to suggest that the atomic configuration of the X center is closely related to that of $V_2,$ and a possible identification of X may be the divacancy-oxygen center ${(V}_2\mathrm{O}).\mathrm{}$