Investigations on the origin of nuclear quadrupole hyperfine parameters of implantedTe125andI129in semiconductors

Recent Mössbauer measurements on ion-implanted ${}_{}{}^{125}{}_{}{}^{}\mathrm{Te}$ and ${}_{}{}^{129}{}_{}{}^{}\mathrm{I}$ in silicon and germanium have provided information about the quadrupole interaction in these systems. Using a model for these systems of an impurity close to one member of a divacancy in the semiconductor and a self-consistent-charge extended Hückel procedure involving a cluster of atoms including the impurity atom, we have analyzed the field gradients at the ${}_{}{}^{125}{}_{}{}^{}\mathrm{Te}$ and ${}_{}{}^{129}{}_{}{}^{}\mathrm{I}$ nuclei. Our analysis supports the proposed model for these impurity systems and provides Te—Si, Te—Ge, I—Si, and I—Ge bond lengths in these systems of 2.49, 2.54, 2.41, and 2.48 Å, respectively. The relationship of these results to measured bond lengths associated with host and adsorbed atoms at surfaces of semiconductors will be discussed.