High-Mobility Carrier Diffusion Visualization and Dynamic Engineering in Bi ₂ O ₂ Se Nanoplates

Bismuth oxychalcogenide (Bi 2 O 2 Se) has emerged as a promising candidate for post-Moore electronics due to its exceptional air stability, high carrier mobility, and integrable high-κ native oxide. However, direct visualization of the spatiotemporal behavior of photoexcited carriers in this two-dimensional layered material remains a fundamental challenge. Here, we overcome this limitation by synergistically combining microtransient absorption spectroscopy with wide-field transient absorption microscopy, enabling real-space imaging of carrier transport in Bi 2 O 2 Se nanoplates. This work uncovers purely linear diffusion with a diffusion coefficient of 11.58 cm 2 /s. Furthermore, a mobility as high as ∼448 cm 2 /(V·s) can be extracted, which is a notably high value for such ultrathin nonencapsulated layered semiconductors. Beyond this quantitative benchmark, our results reveal that thickness and pump fluence serve as decisive knobs for tailoring carrier diffusion and dynamic behavior. Collectively, this work not only advances the mechanistic understanding of carrier dynamics in strongly coupled layered systems but also provides a direct experimental framework to guide future material and device optimization.