Imaging Photocarrier Dynamics in Schottky Junction Interface by Scanning Ultrafast Electron Microscopy

Carrier dynamics at Schottky junction interfaces are crucial for optimizing photoconversion efficiency in photovoltaic, optoelectronic, and photoelectrochemical devices. However, accurately detecting the embedded interfaces remains challenging, particularly with regard to the dynamics of carriers within the two-dimensional (2D) interfacial plane. Here, we use scanning ultrafast electron microscopy (SUEM) to directly image spatiotemporal photocarrier dynamics at the n-type gallium arsenide (n-GaAs)/aluminum (Al) Schottky interface with a nanoscale thickness. The recorded SUEM movies demonstrate that the electrons and holes are separated by the built-in electric field with holes subsequently trapped by interface states. These trapped holes exhibit a quasi-2D subdiffusion behavior along the junction interface via hopping through the interface states. Numerical simulations based on a developed subdiffusion dynamical model well repeat the observations. Our findings provide new insights into the carrier transport dynamics in Schottky junctions and unravel the pivotal role of the interface states.