Unoccupied d states of Au impurities in silicon as studied by x-ray-absorption spectroscopy.

Abstract

Samples of n-type Si(111) were ion implanted with ${10}^{16}$-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ ${\mathrm{Au}}^{+}$ ions at 1 MeV energy, and were then annealed using the rapid-thermal annealing method. Total-electron-yield Au ${\mathit{L}}_{2,3}$ edge x-ray-absorption spectroscopy was used to study the d-orbital structures of a Au atom when it is incorporated into the Si lattice. From near-edge absorption studies, we found that the ``white-line'' areas, relative to bulk Au, of both as-implanted and annealed samples have been significantly increased. The results show that d electrons are depleted when Au interacts with silicon. The estimated Au d-orbital configuration is ${\mathit{d}}^{9.75\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ in ion-amorphized Si, and is ${\mathit{d}}^{9.89\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ in recrystallized Si. (\ensuremath{\delta} is the bulk Au d-hole number). This provides experimental evidence that the d shell of Au impurities does not have the full complement of ten electrons.