Local Structure of S Impurities in GaAs

The local structure of $\mathrm{S}$ implanted in GaAs has been determined by extended x-ray-absorption fine structure by monitoring of the $\mathrm{S}$ $K\alpha$ fluorescence yield. The $\mathrm{S}$ first-neighbor shell shows a significant static broadening compared to the $\mathrm{S}$ second- and third-neighbor shells. This indicates two S configurations of approximately equal population: (1) substitutional $\mathrm{S}$ on an As site and (2) a complex formed by $\mathrm{S}$ on an As site and an As vacancy on the second-neighbor shell with a $\mathrm{S}$-first-neighbor distance relaxation of 0.14 ± 0.04 Å. The two-site configuration explains the disparity between implanted $\mathrm{S}$ concentration and net electrical activity.