A principal cause of THz emission in semiconductor nanostructures is deeply involved with geometry, which stimulates the utilization of indirect bandgap semiconductors for THz applications. To date, applications for optoelectronic devices, such as emitters and detectors, using THz radiation have focused only on direct bandgap materials. This paper reports the first observation of strongly enhanced THz emission from Germanium nanowires (Ge NWs). The origin of THz generation from Ge NWs can be interpreted using two terms: high photoexcited electron-hole carriers (Δn) and strong built-in electric field (E b) at the wire surface based on the relation. The first is related to the extensive surface area needed to trigger an irradiated photon due to high aspect ratio. The second corresponds to the variation of Fermi-level determined by confined surface charges. Moreover, the carrier dynamics of optically excited electrons and holes give rise to phonon emission according to the THz region.
Bibliographical noteFunding Information:
This work was partially supported by the New and Renewable Energy R&D Program (Grant No: 2009T100100614) under the Ministry of Knowledge Economy and Metrology Research Center under Korea Research Institute of Standards and Science. Also, the Yonsei University Research Fund of 2012 for Post doctoral fellowship supported this work.
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