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O: Fachverband Oberflächenphysik

O 74: Ultrafast Electron and Spin Dynamics at Interfaces

O 74.5: Poster

Mittwoch, 9. März 2016, 18:15–20:30, Poster A

Investigation of charge dynamics by optical Pump-Probe Scanning Tunneling Microscopy — •Terence Thias, Philipp Kloth, Katharina Kaiser, and Martin Wenderoth — IV. Physikalisches Institut, Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen

The combination of optical Pump-Probe techniques with Scanning Tunneling Microscopy (STM) enables us to merge atomic resolution of an STM with time resolution on the ns time scale. As it is beyond the bandwidth of the current amplifier we use Shaken-Pulse-Pair-Excitation technique [1]. By illuminating the n-doped GaAs(110) surface we generate electron hole pairs, which will be separated in the tip-induced Space Charge Region (SCR). This results in a hole accumulation layer at the surface. As recent results have shown [2] these holes can serve as an additional tunnel channel into the valence band. Studying the time evolution of the photo-induced tunnel current gives access to the charge dynamics .Surprisingly, we have found a dependency on the pulse duration of excitation as well as on the tunnel current. We discuss two main processes determining the relaxation characteristic of the excited system. One process is the filling of the photo-generated holes trapped at the surface, the other is the charging/discharging of dopants changing the local SCR beneath the STM tip.

[1] Terada et al., Nature Photonics, 4(12), 2010

[2] Kloth et al., Nat. Comm. (2015)