Nano-scale Schottky contacts: ultrafast drift-diffusion dynamics studied in the optical near field

We present direct measurements of the ultrafast carrier dynamics around buried nano-scale Schottky contacts with high spatial and time resolution, performed with a novel femtosecond near-field scanning optical microscope. It is shown that high optically excited carrier densities screen the built-in field around a Schottky contact and allow for efficient transport of electrons towards the contact, followed by trapping of electrons into the metal. The experimental results are modeled by a self-consistent treatment of the drift-diffusion equation for the carriers and Poissonʹs equation for the built-in electric field.