Point defects, doping and the path to n-type SnTe

Point defects in SnTe were studied using first-principles modeling. Sn vacancies were found to be spontaneously formed in SnTe and make it intrinsically a p-type semiconductor, in excellent accord with experiments. The calculated electronic structure for Sn vacancy reveals that the Fermi level is shifted down into the valence band and presents p-type behavior. In contrast, the Fermi level shifts near the conduction band minimum (CBM) for Te vacancy and presents an n-type behavior. All the interstitial sites were considered for a comprehensive intrinsic point defect study. The body-centered (tetrahedral) site was found to be a stable interstitial configuration for Sn, whereas the split<111> interstitial was preferred for Te. We found that the electronic structures due to the interstitial configurations were distinct. Sn interstitials defects, Fermi level was shifted inside the conduction band for body interstitial, near to CBM for split 111 interstitial, whereas inside the bandgap for the base and split 110 interstitial defects. Contrary results were obtained for Te interstitial defects; the Fermi level was found inside the valence band for body interstitial, close to VBM for split 111, while the Fermi level was obtained inside the bandgap for base and split 110 interstitial defects. In addition, extrinsic oxygen impurities and other possible dopants that can transform SnTe to n-type were investigated. Interstitial oxygen was found to be stable at the body-interstitial site and is incorporated easily into the material in both Sn- and Te-rich environments, leading the material to p-type. The Fermi level was obtained inside the bandgap for oxygen substituted in Te vacancy and showed no preferred conductivity behavior. Finally, we find that Sb, Bi, and halogens (in Sn-rich conditions) can significantly improve electron concentrations and be promising dopants to transform the material's intrinsic conductivity from p-type to n-type. Notably, the sample should be prevented from incorporating oxygen impurities while doping sample n-type.