Strongly Enhanced THz Emission caused by Localized Surface Charges in Semiconducting Germanium Nanowires

Abstract

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 (Eb) 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.

Photoconductive response of a single Au nanorod coupled to LaAlO3/SrTiO3 nanowires

“…Such enhancement is directly associated with the plasmonic coupling with induced THz radiation at the junction because the scattering efficiency of AuNR is stronger at parallel polarization conditions. While consistent with previous works on different systems, [34][35][36] this demonstration offers a unique capability to probe single nanoscale objects.…”

Terahertz Emission and Ultrafast Carrier Dynamics of Ar-Ion Implanted Cu(In,Ga)Se2 Thin Films

“…Terahertz (THz) technologies are powerful tools for characterizing the electrodynamics of the carriers and optical properties of semiconductors and nanomaterials nondestructively [8,9]. In the case of THz emission spectroscopy, we can observe the current characteristics and charge transfer of the surface and bulk [10,11]. THz time-domain spectroscopy can be used to measure the optical transmittance, complex optical and dielectric constants, and ac conductivity of matters in the THz frequency region [8,9].…”

Triple phase boundary induced self-catalyzed growth of Ge–graphite core–shell nanowires: field electron emission and surface wettability

“…By this logic, we reasonably hypothesize that other improved functionalities could be also achieved through appropriate design. Although there is much recent interest in the use of 1D Ge nanostructures for many purposes, such as in lithium ion batteries, [9][10][11][12] THz, 13,14 photovoltaics, 15,16 and nanoelectomechanics, 17,18 a simple way to realize Ge nanowire-based core-shell nanostructures is still lacking.…”