Role of native point defects and Hg impurities in the electronic properties of Bi4I4

We studied the effects of point defects and Hg impurities in the electronic properties of bismuth iodide (Bi4I4). Our transport measurements after annealing at different temperatures show that the resistivity of Bi4I4 depends on its thermal history, suggesting that the formation of native defects and impurities can shape the temperature dependence of electrical resistivity. Our density functional theory calculations indicate that the bismuth and iodine antisites and the bismuth vacancies are the dominant native point defects. We find that bismuth antisites introduce resonant states in the band edges, while iodine antisites and bismuth vacancies lead to a n-type and a p-type doping of Bi4I4, respectively. The Hg impurities are likely to be found at Bi substitutional sites, giving rise to the p-type doping of Bi4I4. Overall, our findings indicate that the presence of native point defects and impurities can significantly modify the electronic properties, and, thus, impact the resistivity profile of Bi4I4 due to modifications in the amount and type of carriers, and the associated defect (impurity) scattering. Our results suggest possible routes for pursuing fine-tuning of the electronic properties of quasi-one-dimensional quantum materials. locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon Physics Subject Headings (PhySH)DefectsElectronic structurePoint defectsTopological insulatorsTopological materialsFirst-principles calculationsResistivity measurements