Enhancing Quasi-Two-Dimensional Electronic Structure in Bi₂O₂Se via Chlorine Substitution

Bismuth oxyselenide (Bi₂O₂Se) has emerged as a leading semiconductor candidate for next-generation electronics and quantum phenomena research. However, its strong ionic interlayer bonding of Se layers fundamentally restricts the full potential of this otherwise promising quasi-two-dimensional (2D) material. In this work, we demonstrate chlorine substitution as an effective strategy to introduce van der Waals gaps and modify the electronic structure of the system. Through comprehensive transport and angle-resolved photoemission spectroscopy (ARPES) measurements on Bi₆O₆Se₂Cl₂ single crystal, an optimal Cl-doping compound, we show that the key electronic features, including indirect bandgap, high electron mobility, and carrier effective mass, are well preserved, while the 2D character of the system is sufficiently enhanced. First-principles calculations attribute this selective tunability to the unique spatial separation between conductive Bi-O layers and dopant Se/Cl layers, which enables independent optimization of interlayer coupling and intralayer transport. Remarkably, our theoretical calculations combined with experimental observations project a broad bandgap engineering across a wide range (0.8 ∼ 3.5 eV) within the Bi₂O₂Se system. Our findings not only expand the application potential of Bi₂O₂Se-based materials in optoelectronics, nanoelectronics, and fundamental research but also highlight spatial decoupling as a viable strategy for modifying the detailed electronic structure of quasi-2D quantum systems.