Atomically thin two-dimensional (2D) materials are expected to extend the scaling limits of conventional silicon-based devices due to their planar structure, unique properties, and versatile device applications, which have attracted considerable interest from the scientific and industrial communities. In recent decades, much attention has been focused on “classic” 2D materials, e.g., graphene (Gr), transition metal dichalcogenides (TMDs), black phosphorous (BP), silicene, perovskites, MXenes, etc. Among enormous 2D materials, atomically thin 2D bismuth oxyselenides (Bi₂O₂Se) semiconductors have recently attracted extensive attention from the material research community owing to their unique structure, excellent long-term environmental stability, and high carrier mobility, which makes them ideal candidates for advanced electronic and optoelectronic applications. In this dissertation, single-crystalline ultrathin Bi₂O₂Se nanoflakes are controllably synthesized by using chemical vapor deposition (CVD) method, and more importantly, high-performance electronics/optoelectronic applications based on their interesting fundamental physical characteristics have been systematically explored.

First, a hydromechanical strategy for achieving the aligned epitaxy of 2D materials on vdWs mica dielectrics, coordinated with Simcenter STAR CMM+ simulation, is developed for the promising high-quality synthesis of large-scale 2D films via the coalescence process. In order to better understand the epitaxial relationship between the 2D material and the sixfold vdWs dielectric, a systematic theoretical analysis was performed by combining the density functional theory (DFT) calculation with Lagrange's group theorem. After that, an unreported criterion for how the epitaxial growth of the 2D material on a sixfold symmetric vdWs dielectric is established. In addition, this dissertation presents reproducible techniques to manipulate epitaxially grown 2D materials on pristine vdWs mica dielectrics with high precision and evaluates the electrical properties of ultrathin epitaxially grown Bi₂O₂Se-based FETs supported on pristine vdWs epitaxial substrates at the device level. These results provide a powerful methodological platform for aligned 2D material synthesis, alignment direction prediction, and intrinsic property investigation, laying the foundation for advanced electronics on as-grown 2D materials/vdWs dielectrics.

Furthermore, the ferroelectricity and electronic characteristics of the ultrathin Bi₂O₂Se flakes synthesized by the CVD method are systematically investigated. The piezoresponse force microscopy (PFM) investigated the out-of-plane (OOP) ferroelectric polarization of the ultrathin Bi₂O₂Se with a thickness down to 7.3 nm. A systematic theoretical analysis, combining ab initio molecular dynamics (AIMD) simulation with the DFT calculation, is performed to gain deep insight into its ferroelectric origin and electrically ferroelectric polarization switching. The device-level interplay between ferroelectricity and electronic characteristics was investigated using the 2D Bi₂O₂Se ferroelectric semiconductor field-effect transistors (FeS-FETs). Moreover, a unique ferroelectric semiconductor photodetector (FeS-PD) with nonvolatile functionality and controllability is developed owing to the reproducibility of remnant polarization switching in ferroelectric semiconductors. These results demonstrate that ferroelectric and semiconducting properties can work together in Bi₂O₂Se, laying the groundwork for integrating sensing, logic, and memory functions into a single material system that could help overcome the bottlenecks of von Neumann architectures.