Radiation defects in ion-implanted silicon. II. Mössbauer spectroscopy ofSn119defect structures from implantations of radioactive tellurium

Abstract

Defect structures containing Sn impurity atoms in silicon have been studied by M\"ossbauer emission spectroscopy on the 24-keV transition of $^{119}\mathrm{Sn}$. The defects have been produced by ion implantation of radioactive $^{119m}\mathrm{Te}$. This decays via the decay chain $^{119m}\mathrm{Te}\ensuremath{\rightarrow}^{119}\mathrm{Sb}\ensuremath{\rightarrow}^{119}\mathrm{Sn}$ to the M\"ossbauer level of $^{119}\mathrm{Sn}$. In the M\"ossbauer spectra the $^{119}\mathrm{Sn}$ atoms yield six different lines, characterized primarily by their isomer shifts and Debye-Waller factors. The existence of six independent lines and some of their properties are established experimentally by varying implantation dose and temperature, from postimplantations of other selected isotopes, from implantations in silicon crystals with a range of oxygen concentrations, and from annealing experiments. The lines have been attributed to different Sn bonding configurations and assigned to several lattice locations of the impurity atoms. In all spectra the line characteristic of substitutional Sn atoms was observed (isomer shift: $\ensuremath{\delta}=1.84$ mm/s, Debye temperature: $\ensuremath{\Theta}=250$ K). Large fractions of the impurity atoms are found in vacancy associated defect structures. Different impurity-vacancy complexes have been distinguished from the isomer shifts (electronic configurations) and Debye temperatures of the Sn impurity atoms ($\ensuremath{\delta}=2.6$ mm/s, $\ensuremath{\Theta}=165 or 250$ K, and $\ensuremath{\delta}=0.9$ mm/s, $\ensuremath{\Theta}=230$ K). Possible configurations of these complex defects are discussed. A minor fraction of the Sn atoms ($\ensuremath{\delta}=3.3$ mm/s, $\ensuremath{\Theta}=250$ K) is concluded to be in an interstitial position, probably in an agglomerate. A line ($\ensuremath{\delta}=4.4$ mm/s and $\ensuremath{\Theta}=175$ K) correlated with the oxygen content of the sample is assigned to a complex defect structure containing oxygen atoms. From the implantation and annealing experiments, conclusions on properties of the Te and Sb parents can be drawn. The fraction of Te atoms ending on undisturbed substitutional sites is found to vary with the implantation temperature (\ensuremath{\sim}70 at.% for 670 K and \ensuremath{\sim}30 at.% for room-temperature implantations). The remaining atoms are distributed in different defect structures. Annealing of room-temperature-implanted samples up to \ensuremath{\sim}1200 K did not change the Te-atoms locations substantially. Thus, defect structures containing Te atoms are concluded to be unusually stable. In contrast to this, the related defect structures containing Sb atoms from the radioactive decay of Te can be annealed at temperatures between 500 and 900 K.