Tin-vacancy acceptor levels in electron-irradiated n-type silicon

Si crystals (n-type, fz) with doping levels between $1.5\times {10}^{14}$ and $2\times {10}^{16}{\mathrm{cm}}^{\mathrm{-}3}$ containing in addition $\sim {10}^{18}{\mathrm{S}\mathrm{n}/\mathrm{c}\mathrm{m}}^3$ were irradiated with 2-MeV electrons to different doses and subsequently studied by deep level transient spectroscopy, Mössbauer spectroscopy, and positron annihilation. Two tin-vacancy (Sn-V) levels at $E_c-0.214\mathrm{eV}$ and $E_c-0.501\mathrm{eV}$ have been identified ${(E}_c$ denotes the conduction band edge). Based on investigations of the temperature dependence of the electron-capture cross sections, the electric-field dependence of the electron emissivity, the anneal temperature, and the defect-introduction rate, it is concluded that these levels are the double and single acceptor levels, respectively, of the Sn-V pair. These conclusions are in agreement with electronic structure calculations carried out using a local spin-density functional theory, incorporating pseudopotentials to eliminate the core electrons, and applied to large H-terminated clusters. Thus, the Sn-V pair in Si has five different charge states corresponding to four levels in the band gap.