Gas doping on the topological insulator Bi₂Se₃ surface

Gas molecule doping on the topological insulator Bi₂Se ₃ surface with existing Se vacancies is investigated using first-principles calculations. Consistent with experiments, NO₂ and O₂ are found to occupy the Se vacancy sites, remove vacancy-doped electrons, and restore the band structure of a perfect surface. In contrast, NO and H₂ do not favor passivation of such vacancies. Interestingly we have revealed a NO₂ dissociation process that can well explain the speculative introduced "photon-doping" effect reported by recent experiments. Experimental strategies to validate this mechanism are presented. The choice and the effect of different passivators are discussed. This step paves the way for the usage of such materials in device applications utilizing robust topological surface states.