Density functional theory calculations of intrinsic defects in PbTe

PbTe is very noteworthy thermoelectric material working at intermediate temperatures. Most investigations of PbTe were focused on PbTe-based alloys to control band convergence, formation of resonant level, and nanostructuring. However, the intrinsic-defect nature of PbTe is still not well understood yet. The semiconductor type of PbTe-related alloys is known to be determined by Pb concentration with respect to Te concentration. In binary, Pb-rich or Te-rich PbTe typically exhibits n-type or p-type behavior, respectively. Our experiments showed that 10% excess-Pb doping merely changes the lattice parameter (<+0.3%). To understand such atomic and electrical behaviors in off-stoichiometric PbTe, we theoretically investigated the formation of intrinsic defects in PbTe by performing first-principle density functional theory calculations. We used PAW method and GGA-PBE, which are implemented in VASP code. The defect formation energies of various charged states were computed on the 128-atom FCC supercell and a 3x3x3 k-point mesh. We suggest that the formation of Pb interstitial or Te vacancy might be responsible for the off-stoichiometry in Pb-rich PbTe, while the formation of Pb vacancy or Te vacancy might be responsible in Te-rich PbTe.