Pulses of coherent terahertz radiation can be efficiently generated by a lateral diffusion current after ultrafast generation of photo-carriers near a metal interface on the surface of a semiconductor, this is known as the lateral photo-Dember effect. We investigate how the emission depends on the pump spot position, size, power and how it is affected by the application of an applied external bias. We study the role of the metallic mask and how it suppresses emission from the carriers diffusing under it due to a reduction of available radiation states both theoretically and experimentally.
Terahertz (THz) radiation can be generated by ultrafast photo-excitation of carriers in a semiconductor partly masked by a gold surface. A simulation of the effect taking into account the diffusion of carriers and the electric field shows that the total net current is approximately zero and cannot account for the THz radiation. Finite element modelling and analytic calculations indicate that the THz emission arises because the metal inhibits the radiation from part of the dipole population, thus creating an asymmetry and therefore a net current. Experimental investigations confirm the simulations and show that metal-mask dipole inhibition can be used to create THz emitters.
We demonstrate multiplexed terahertz emitters that exhibits 2 THz bandwidth
that do not require an external bias. The emitters operate under uniform
illumination eliminating the need for a micro-lens array and are fabricated
with periodic Au and Pb structures on GaAs. Terahertz emission originates from
the lateral photo-Dember effect and from the different Schottky barrier heights
of the chosen metal pair. We characterize the emitters and determine that most
terahertz emission at 300 K is due to band-bending due to the Schottky barrier
of the metal.Comment: 4 pages, 6 figure
We characterise THz output of lateral photo-Dember (LPD) emitters based on semi-insulating (SI), unannealed and annealed low temperature grown (LTG) GaAs. Saturation of THz pulse power with optical fluence is observed, with unannealed LTG GaAs showing highest saturation fluence at 1.1 ± 0.1 mJ cm −2 . SI-GaAs LPD emitters show a flip in signal polarity with optical fluence that is attributed to THz emission from the metal-semiconductor contact. Variation in optical polarisation affects THz pulse power that is attributed to a local optical excitation near the metal contact.
Multiplexed gallium-arsenide (GaAs)-based terahertz (THz) emitters fabricated with periodic double-metal structures are demonstrated and the effect of different metals on the THz output is investigated. THz emission originates from the lateral photo-Dember effect and from the different Schottky barrier heights of the chosen metal pair. The metal combinations used were Au-Al, Au-Pb and Cu-Cr. The emitters were characterised according to temperature and the highest peak-to-peak THz emission was achieved with the Cu-Cr metal pairing at 150 K.Introduction: Lateral photo-Dember (LPD) emitters have been demonstrated to be robust terahertz (THz) emitters that require no voltage bias to operate [1-3]. An LPD emitter is fabricated by partially masking a semiconductor surface with a deposited metal layer. An ultrafast laser, with above band-gap energy, is focused on the metal-semiconductor boundary. An asymmetrical distribution of photo-generated carriers that are free to diffuse is created near the metal-semiconductor interface. The carriers that diffuse beneath the metal mask form a dipole (dipole B in Fig. 1a), which is quenched due to reflection from the metal surface [4], whereas the carriers that diffuse away from the metal form a dipole (dipole A in Fig. 1a) that is free to radiate and does so parallel to the pump beam.
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