Strategic Chemical Vapor Deposition of Two‐Dimensional Bismuth Oxyselenide

ABSTRACT Two‐dimensional (2D) bismuth oxyselenide (Bi 2 O 2 Se) has recently emerged as a promising material due to its exceptional carrier mobility, photodetectivity, and surface sensitivity, making it highly attractive for future electronic and optoelectronic applications. Among various synthesis methods, chemical vapor deposition (CVD) stands out as an optimal approach for fabricating 2D Bi 2 O 2 Se, owing to its scalability, controllability, cost‐effectiveness, and high efficiency. Despite its potential, understanding the growth kinetics of 2D Bi 2 O 2 Se via CVD remains limited. In this study, we strategically investigate the CVD growth behavior under a range of conditions, including substrate selection, growth duration, precursor ratio modulation (Se/Bi 2 O 3 ), a comparison between one‐step and two‐step growth processes, and the orientation of substrates (horizontal vs. vertical). We successfully achieved epitaxial growth of 2D Bi 2 O 2 Se on SrTiO 3 (100) substrates and explored key factors such as the relationship between growth time and lateral flake size, the influence of substrate roughness and wettability (hydrophilicity/hydrophobicity), and the effects of substrate lateral and vertical orientations on growth morphology. Notably, we demonstrate a two‐step CVD strategy involving Bi 2 O 3 pre‐deposition followed by selenization, which enables the formation of 2D Bi 2 O 2 Se flakes. Our findings provide valuable insights into the CVD synthesis of 2D Bi 2 O 2 Se and offer a foundation for advancing its integration into next‐generation electronic and optoelectronic devices.