Competing Surface and Subsurface Carrier Dynamics Resolved by Voltage-Tunable Scanning Ultrafast Electron Microscopy

) enables effective depth-selective probing to spatially disentangle these competing dynamics within the near-surface region. Experiments on p-type silicon reveal a striking voltage-tunable contrast inversion, marking a transition from surface-dominated to subsurface-dominated regimes. We attribute this to a mechanistic competition between surface potential restoration governing collection and subsurface band flattening modulating emission. Multiphysics simulations confirm this framework by linking depth-dependent charge distributions to contrast evolution. We thus achieve independent visualization of spatially entangled processes, specifically isolating surface trapping from subsurface diffusion and providing a physical basis for resolving vertical carrier stratification.