Step‐Climbing Epitaxy of Layered Materials with Giant Out‐of‐Plane Lattice Mismatch

Abstract Heteroepitaxy with large lattice mismatch remains a great challenge for high‐quality epifilm growth. Although great efforts have been devoted to epifilm growth with an in‐plane lattice mismatch, the epitaxy of 2D layered crystals on stepped substrates with a giant out‐of‐plane lattice mismatch is seldom reported. Here, taking the molecular‐beam epitaxy of 2D semiconducting Bi₂O₂Se on 3D SrTiO₃ substrates as an example, a step‐climbing epitaxy growth strategy is proposed, in which the n‐th (n = 1, 2, 3…) epilayer climbs the step with height difference from out‐of‐plane lattice mismatch and continues to grow the n+1‐th epilayer. Step‐climbing epitaxy can spontaneously relax and release the strain from the out‐of‐plane lattice mismatch, which ensures the high quality of large‐area epitaxial films. Wafer‐scale uniform 2D Bi₂O₂Se single‐crystal films with controllable thickness can be obtained via step‐climbing epitaxy. Most notably, one‐unit‐cell Bi₂O₂Se films (1.2 nm thick) exhibit a high Hall mobility of 180 cm² V⁻¹ s⁻¹ at room temperature, which exceeds that of silicon and other 2D semiconductors with comparable thickness. As an out‐of‐plane lattice mismatch is generally present in the epitaxy of layered materials, the step‐climbing epitaxy strategy expands the existing epitaxial growth theory and provides guidance toward the high‐quality synthesis of layered materials.