Layer-Controlled Growth of Single-Crystalline 2D Bi₂O₂Se Film Driven by Interfacial Reconstruction

As semiconductor scaling continues to reach sub-nanometer levels, two-dimensional (2D) semiconductors are emerging as a promising candidate for the post-silicon material. Among these alternatives, Bi₂O₂Se has risen as an exceptionally promising 2D semiconductor thanks to its excellent electrical properties, attributed to its appropriate bandgap and small effective mass. However, unlike other 2D materials, growth of large-scale Bi₂O₂Se films with precise layer control is still challenging due to its large surface energy caused by relatively strong interlayer electrostatic interactions. Here, we present the successful growth of a wafer-scale (∼3 cm) Bi₂O₂Se film with precise thickness control down to the monolayer level on TiO₂-terminated SrTiO₃ using metal-organic chemical vapor deposition (MOCVD). Scanning transmission electron microscopy (STEM) analysis confirmed the formation of a [BiTiO₄]^1- interfacial structure, and density functional theory (DFT) calculations revealed that the formation of [BiTiO₄]^1- significantly reduced the interfacial energy between Bi₂O₂Se and SrTiO₃, thereby promoting 2D growth. Additionally, spectral responsivity measurements of two-terminal devices confirmed a bandgap increase of up to 1.9 eV in monolayer Bi₂O₂Se, which is consistent with our DFT calculations. Finally, we demonstrated high-performance Bi₂O₂Se field-effect transistor (FET) arrays, exhibiting an excellent average electron mobility of 56.29 cm²/(V·s). This process is anticipated to enable wafer-scale applications of 2D Bi₂O₂Se and facilitate exploration of intriguing physical phenomena in confined 2D systems.