Low Surface Recombination Velocity and Enhanced Photocarrier Dynamics in Bi ₂ O ₂ Se Nanosheets

Abstract Among 2D materials, the layered semiconductor Bi ₂ O ₂ Se stands out due to its unique electrostatically bonded layered structure without a van der Waals gap, making it a promising candidate for various electronic, optoelectronic, and photonic applications. This potential is largely attributed to its exceptional properties, including ultrahigh electron mobility and stability. While surface effects are known to significantly influence carrier transport in low‐dimensional materials, the impact of dimensionality on photocarrier dynamics remains unexplored. In this study, ultrafast broadband pump–probe spectroscopy is utilized to directly investigate surface recombination as a key factor governing photocarrier dynamics in Bi ₂ O ₂ Se. The findings reveal a bulk lifetime of 1.6 ns and a surface‐recombination velocity ( S ) of 1.84 ± 0.02 × 10 ³ cm s ⁻¹ , which is significantly lower than that observed in other unpassivated 2 and 3D semiconductors. This low S value suggests a promising avenue for enhanced photocarrier lifetime and high efficiency, even at ultrathin nanoscales. These observations provide insight into the critical role of material thickness in device performance and highlight potential advantages of surface passivation, thereby broadening the application potential of Bi ₂ O ₂ Se in next‐generation ultrathin electronics, optoelectronics, and photonic devices.