Regensburg 2007 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 13: Poster 1

HL 13.33: Poster

Montag, 26. März 2007, 15:00–17:30, Poster A

Terahertz Emission by Drift and Diffusion — •Guillermo Acuna, Federico Buersgens, Christian Lang, and Roland Kersting — University of Munich, Munich, Germany

Many charge carrier dynamics that follow femtosecond laser excitation can be used to generate terahertz (THz) radiation in semiconductors. Examples are the ultrafast onset of current surges in an electric field or the Dember effect, which arises due to different electron and hole diffusivities. The individual contributions to the emitted THz signal are still under discussion. In this work we present an experiment that gives quantitative insight into the charge carrier dynamics that lead to THz emission. We perform time resolved THz studies on a semi-insulating GaAs structure with periodically poled surface electrodes. The emission processes are distinguished by their dependence on the applied electrical field. Most surprising is that the THz signal depends on the applied electrical field, although the alternating direction of the driving field should lead to a cancellation of the far-field emission. This emission process is explained by electron acceleration in regions with inhomogeneous fields. Other dynamics that become visible by their specific terahertz emission are the Dember effect, the intervalley transfer of electrons, and the hole current at high field strengths.