Unoccupieddstates of Au impurities in silicon as studied by x-ray-absorption spectroscopy

Samples of n-type Si(111) were ion implanted with 10¹⁶-cm^-2 Au⁺ ions at 1 MeV energy, and were then annealed using the rapid-thermal annealing method. Total-electron-yield Au L2,3 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 d^9.75-δ in ion-amorphized Si, and is d^9.89-δ in recrystallized Si. ({δ} 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.