Layer-Controlled Growth of Single-Crystalline 2D Bi 2 O 2 Se 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, Bi 2 O 2 Se 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 Bi 2 O 2 Se 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) Bi 2 O 2 Se film with precise thickness control down to the monolayer level on TiO 2 -terminated SrTiO 3 using metal-organic chemical vapor deposition (MOCVD). Scanning transmission electron microscopy (STEM) analysis confirmed the formation of a [BiTiO 4 ] 1- interfacial structure, and density functional theory (DFT) calculations revealed that the formation of [BiTiO 4 ] 1- significantly reduced the interfacial energy between Bi 2 O 2 Se and SrTiO 3 , thereby promoting 2D growth. Additionally, spectral responsivity measurements of two-terminal devices confirmed a bandgap increase of up to 1.9 eV in monolayer Bi 2 O 2 Se, which is consistent with our DFT calculations. Finally, we demonstrated high-performance Bi 2 O 2 Se field-effect transistor (FET) arrays, exhibiting an excellent average electron mobility of 56.29 cm 2 /(V·s). This process is anticipated to enable wafer-scale applications of 2D Bi 2 O 2 Se and facilitate exploration of intriguing physical phenomena in confined 2D systems.