Highly Conducting, n-Type Bi₁₂O₁₅Cl₆ Nanosheets with Superlattice-like Structure

Modulating the type and magnitude of electrical conductivity remains a basic requirement for a semiconductor's widespread acceptability and use. Here, we convert nanosheets of BiOCl, a V-VI-VII ternary semiconductor, to an oxygen-rich Bi₁₂O₁₅Cl₆ phase. In the process, the intrinsic conductivity switches from p-type to n-type. The phase change is achieved using a vacuum annealing step at 500°C for 1 h. BiOCl nanosheets convert to the Bi₁₂O₁₅Cl₆ phase via volatilization of BiCl₃ resulting in a unique superlattice like structure with a periodicity of 1.48 nm. Correspondingly, the band gap decreases from 3.41 to 2.48 eV from the raising of the valence band edge. Activation energy for electrical conductivity reduces from 862 meV for BiOCl to 778 meV for Bi₁₂O₁₅Cl₆, and a corresponding photoconductivity increase of 80× is observed. Density functional theory calculations predict changes to the valence band and increase in the Fermi level toward the conduction band edge for the Bi₁₂O₁₅Cl₆ nanosheets - in accordance with experimental data. The availability of both p- and n-type ternary semiconducting systems widen the application base for Bi-O-Cl based materials.