Revealing Dopant Local Structure of Se-Doped Black Phosphorus

Black phosphorus has been reported as a remarkable 2D material due to its unique electrical, optical, and thermal properties, leading to promising device applications in optics, thermoelectricity, physics, material science, and energy storage. Indeed, the intrinsic band structure of black phosphorus is adjustable through doping various heteroatoms to further improve the electrical and optical performance. However, it is difficult for traditional characterization methods (e.g., X-ray diffraction or X-ray photoelectron spectroscopy) to give a clear picture of the local structure around the dopant atoms. To solve this problem, we have applied synchrotron based X-ray absorption spectroscopy techniques like X-ray absorption near edge structure and extended X-ray absorption fine structure combined with density functional theory calculations to reveal the local structure around the Se dopant in Se-doped BP. It is found that Se exists as both dopant and pure Se in Se-doped BP, while the ratio of dopant to pure Se increases with increasing Se content in the raw material. This is the first confirmation of the coexistence of two dopant element phases in the doped-BP literature. Meanwhile, the introduction of Se successfully decreases the bandgap and resistivity of BP. In addition, the bandgap and resistivity can be further reduced by increasing the amount of Se.