title: Ultrafast dynamics. Four-dimensional imaging of carrier interface dynamics in p-n junctions.
abstract: The dynamics of charge transfer at interfaces are fundamental to the understanding of many processes, including light conversion to chemical energy. Here, we report imaging of charge carrier excitation, transport, and recombination in a silicon p-n junction, where the interface is well defined on the nanoscale. The recorded images elucidate the spatiotemporal behavior of carrier density after optical excitation. We show that carrier separation in the p-n junction extends far beyond the depletion layer, contrary to the expected results from the widely accepted drift-diffusion model, and that localization of carrier density across the junction takes place for up to tens of nanoseconds, depending on the laser fluence. The observations reveal a ballistic-type motion, and we provide a model that accounts for the spatiotemporal density localization across the junction.
authors.affiliation: Physical Biology Center for Ultrafast Science and Technology, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: Ebrahim
authors.initials: E
authors.lastname: Najafi
authors.affiliation: Physical Biology Center for Ultrafast Science and Technology, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Scarborough
authors.affiliation: Physical Biology Center for Ultrafast Science and Technology, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125, USA. Institute of Photonics, National Chiao Tung University, 300 Hsinchu, Taiwan.
authors.forename: Jau
authors.initials: J
authors.lastname: Tang
authors.affiliation: Physical Biology Center for Ultrafast Science and Technology, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125, USA. zewail@caltech.edu.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Zewail