Chemical Vapor Deposition Growth of Two-Dimensional Bi₄Se₃ with Robust Ferroelectricity

Bi 4 Se 3 is a topological superlattice material that has been extensively studied for applications in catalysis, photovoltaics, and thermoelectrics. However, existing methods typically yield Bi 4 Se 3 polycrystalline films with nonhomogeneous phases, significantly limiting their use in electronic devices. In this study, we demonstrate the chemical vapor deposition (CVD) growth of two-dimensional (2D) single-crystal Bi 4 Se 3 with a lateral size up to 20 μm and a thickness as thin as 4 nm. The growth process involves the formation of a Bi 2 O 2 layer, which promotes the development of [Bi 2 Se 3 ·Bi 2 O x ] and facilitates the release of oxygen atoms at elevated temperatures. Notably, optical second harmonic generation (SHG) characterization reveals the noncentrosymmetric structure of the 2D Bi 4 Se 3 . Furthermore, at room temperature, switchable out-of-plane ferroelectric polarization was observed in 2D Bi 4 Se 3 . Finally, double-ended memory resistor measurements of the Bi 4 Se 3 -based device demonstrate a large switching ratio of approximately 10 4 within a voltage range of 2.5 V and a retention time exceeding 270 s. This work provides a method for synthesizing single-crystal Bi 4 Se 3 and highlights its robust ferroelectricity, offering potential for applications in ferroelectric nonvolatile devices.