Multiple double-metal bias-free terahertz emitters

McBryde, Duncan; Gow, Paul C.; Berry, Sam A.; Barnes, M. E.; Aghajani, Armen; Apostolopoulos, Vasileios

doi:10.1063/1.4878739

Cited by 11 publications

(13 citation statements)

References 20 publications

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“…The same group presented a simple but robust LPD device concept using metal stripes with two different thicknesses, one of which thin enough to be transparent for THz radiation. 13 This arrangement can be easily multiplexed, and the efficiency of this concept has been demonstrated experimentally. Moreover, by choosing mask metals that form different Schottky barrier heights, lateral electric fields can be induced at the emitter surface in which lateral photocurrents can be driven.…”

Section: Introductionmentioning

confidence: 99%

“…10 Recently, lateral photo-Dember (LPD) emitters have been demonstrated, in which the photogenerated electrons move parallel to the semiconductor surface and the generated THz radiation is effectively coupled out. 4,[11][12][13] It has been shown that the efficiency of LPD emitters is comparable to those of PC emitters with the additional advantage of biasfree operation. 11 However, there has been a debate on the physical origin for the strong THz emission from LPD devices.…”

Section: Introductionmentioning

confidence: 99%

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Bias-free lateral terahertz emitters—A simulation study

Granzner

Polyakov

Cimalla

et al. 2015

Journal of Applied Physics

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The design and performance of bias-free InN-based THz emitters that exploit lateral photocurrents is studied by means of numerical simulations. We use a drift-diffusion model with adjusted carrier temperatures and mobilities. The applicability of this approach is demonstrated by a comparison with results from Monte-Carlo simulations. We consider a simple but robust lateral emitter concept using metal stripes with two different thicknesses with one of them being thin enough to be transparent for THz radiation. This arrangement can be easily multiplexed and the efficiency of this concept has already been demonstrated by experiment for GaAs substrates. In the present study, we consider InN, which is known to be an efficient photo-Dember emitter because of its superior transport properties. Our main focus is on the impact of the emitter design on the emission efficiency assuming different operation principles. Both the lateral photo-Dember (LPD) effect and built-in lateral field effects are considered. The appropriate choice of the metal stripe and window geometry as well as the impact of surface Fermi level pinning are investigated in detail, and design guidelines for efficient large area emitters using multiplexed structures are provided. We find that InN LPD emitters do not suffer from Fermi level pinning at the InN surface. The optimum emission efficiency is found for LPD emitter structures having 200 nm wide illumination windows and mask stripes. Emitter structures in which lateral electric fields are induced by the metal mask contacts can have a considerably higher efficiency than pure LPD emitters. In the best case, the THz emission of such structures is increased by one order of magnitude. Their optimum window size is 1 lm without the necessity of a partially transparent set of mask stripes. V C 2015 AIP Publishing LLC.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Bias-free lateral terahertz emitters—A simulation study

Granzner

Polyakov

Cimalla

et al. 2015

Journal of Applied Physics

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“…These emitters come in the form of continuous layers 9,10 or, recently, 11,12 in the form of discontinuous periodic structures where in addition to in-plane Schottky-field induced THz emission, the lateral photo-dember effect plays a role.…”

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confidence: 99%

Enhanced Terahertz Emission from Schottky Junctions Using Plasmonic Nanostructures

2014

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We present measurements of the enhanced emission of terahertz pulses after the optical excitation of grating-coupled near-IR surface plasmons at the interface of gold and cuprous oxide, using femtosecond laser pulses. Terahertz emission is the result of the acceleration of charge carriers optically excited in the Schottky depletion field of the metal/semiconductor interface. The enhancement is a direct consequence of the localized nature of the surface plasmon field, which is strongest near the nanostructured metal surface where the Schottky electric field is strongest too. Surface plasmon excitation is confirmed by reflection spectroscopy of gratings with different periods, by varying the azimuthal angle of the grating, and by calculations of the plasmon frequencies and fields. We observe a terahertz field enhancement factor of 5.8 when compared to the emission from a flat sample. This corresponds to a THz power-enhancement factor of 34. Our results show that for THz emission from these metal/semiconductor interfaces, it matters more where the pump light is absorbed than how much pump light is absorbed.

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“…The substrate material is semi-insulating GaAs. The fabrication and characterization of the emitters is described in [20,21]. Two DM emitters with the above geometry were fabricated for the experiments, one with circular emitter elements to generate radial polarization and one emitter with straight elements that was used for the measurement of angular emission dependence and the focusing experiments.…”

Section: Fabrication Of Emittersmentioning

confidence: 99%

“…This paper explores beam steering using large-area emitters that generate THz radiation via diffusion currents, also known as the lateral photo-Dember (LPD) effect [17][18][19] and Schottky potentials [20,21]. LPD and Schottky potential-based double metallic emitters have been found to have similar spectral bandwidth with photo-conductive emitters [19,20] . Various THz sources have been assessed for their capability to be implemented in a phase-delay array, but in-depth studies of a scheme using LPD emitters has yet to be tested.…”

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confidence: 99%

Terahertz Focusing and Polarization Control in Large-Area Bias-Free Semiconductor Emitters

Carthy

Gow

Berry

et al. 2017

J Infrared Milli Terahz Waves

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We show that, when large-area multiplex terahertz semiconductor emitters, that work on diffusion currents and Schottky potentials, are illuminated by ultrashort optical pulses they can radiate a directional electromagnetic terahertz pulse which is controlled by the angular spectrum of the incident optical beam. Using the lens that focuses the incident near-infrared pulse, we have demonstrated THz emission focusing in free space, at the same point where the optical radiation would focus. We investigated the beam waist and Gouy phase shift of the THz emission as a function of frequency. We also show that the polarization profile of the emitted THz can be tailored by the metallic patterning on the semiconductor, demonstrating radial polarization when a circular emitter design is used. Our techniques can be used for fast THz beam steering and mode control for efficiently coupling to waveguides without the need for THz lenses or parabolic mirrors.

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Multiple double-metal bias-free terahertz emitters

Cited by 11 publications

References 20 publications

Bias-free lateral terahertz emitters—A simulation study

Bias-free lateral terahertz emitters—A simulation study

Enhanced Terahertz Emission from Schottky Junctions Using Plasmonic Nanostructures

Terahertz Focusing and Polarization Control in Large-Area Bias-Free Semiconductor Emitters

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