Local structure analysis of Sb, Bi, and Ag dopant atoms in Mg2Si semiconductor by x-ray absorption spectroscopy and first-principles calculation

Abstract

The local structures around Sb, Bi, and Ag dopant atoms in the environmentally friendly semiconductor Mg2Si were investigated by Sb K-edge, Bi L3-edge, and Ag K-edge x-ray absorption spectroscopy performed at 10 K. Fourier transforms (FTs) of the k3-weighted extended x-ray absorption fine structure (EXAFS) were analyzed. The experimental FTs of k3-weighted EXAFS were compared with the results of calculations using model clusters with Sb, Bi, and Ag atoms at the 8c, 4a, and 4b sites. The inverse FT of the χ(R) spectrum was calculated to refine the local structures for neighboring atoms around the Sb, Bi, and Ag atoms, and the interatomic distances and Debye–Waller factors were determined from the fit of the inverse FTs. The occupation of the 4a site by Sb and Bi atoms was demonstrated and that of the 8c site was investigated for Ag atoms. First-principles calculations were performed to clarify the characteristic change in the second-neighbor distances around the Ag atoms. The evaluation of the crystal orbital Hamilton population clarified that the change in the second-neighbor distances is caused by the bonding character formed between the Ag and Mg atoms. These results suggest that the Ag atoms mainly occupy the 8c site, while the large value of the Debye–Waller factor for the second neighboring atoms implies the possibility of the partial occupation of Ag atoms at the 4b sites. These findings provide an explanation for limiting the p-type conductivity in Mg2Si semiconductors.