Abstract-Terahertz detection by epitaxial-graphene field-effect-transistors on silicon carbide

F. Bianco^1,a), D. Perenzoni², D. Convertino³, S. L. De Bonis^1,b), D. Spirito^1,c),M. Perenzoni², C. Coletti³, M. S. Vitiello¹ and A. Tredicucci^2,4
 HIDE AFFILIATIONS
1 NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza S. Silvestro 12, 56127 Pisa, Italy
2 Fondazione Bruno Kessler (FBK), Via Sommarive 18, 38123 Povo, Trento, Italy
3 CNI@NEST, Istituto Italiano di Tecnologia, Piazza S. Silvestro 12, 56127 Pisa, Italy
4 NEST, Istituto Nanoscienze-CNR and Dipartimento di Fisica “E. Fermi”, Università di Pisa, Largo Bruno Pontecorvo 3, 56127 Pisa, Italy
a) Author to whom correspondence should be addressed. Electronic mail: federicabianco82@gmail.com
b) Present address: ICFO, Av. Carl Friedrich Gauss, Centre d'Investigació en Nanociència, Castelldefels, Barcelona 08860, Spain.
c) Present address: Istituto Italiano di Tecnologia, Nanochemistry department and Graphene labs, Via Morego 30, 16163 Genova, Italy.
Appl. Phys. Lett. 107, 131104 (2015); http://dx.doi.org/10.1063/1.4932091

http://scitation.aip.org/content/aip/journal/apl/107/13/10.1063/1.4932091?TRACK=RSS

We report on room temperature detection of terahertz radiation by means of antenna-coupledfield effect transistors (FETs) fabricated using epitaxial graphene grown on silicon carbide. The achieved photoresponsivity (∼0.25 V/W) and noise equivalent power (∼80 nW/ Hz−−−√ ) result from the combined effect of two independent detection mechanisms: over-damped plasma wave rectification and thermoelectric effects, the latter ascribed to the presence of carrier density junctions along the FET channel. The calculated plasmonic and thermoelectric response reproduces qualitatively well the measured photovoltages; the experimentally observed sign-switch demonstrates the stronger contribution of plasmonic detection compared to the thermoelectric one. These results unveil the potential of plasmonic detectors exploitingepitaxial graphene on silicon carbide for fast large area imaging of macroscopic samples.

Abstract-High-Q resonant cavities for terahertz quantum cascade lasers

High-Q resonant cavities for terahertz quantum cascade lasers A. Campa, L. Consolino, M. Ravaro, D. Mazzotti, M. S. Vitiello, S. Bartalini, and P. De Natale  »View Author Affiliations http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-23-3-3751

Optics Express, Vol. 23, Issue 3, pp. 3751-3761 (2015)
http://dx.doi.org/10.1364/OE.23.003751

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We report on the realization and characterization of two different designs for resonant THz cavities, based on wire-grid polarizers as input/output couplers, and injected by a continuous-wave quantum cascade laser (QCL) emitting at 2.55 THz. A comparison between the measured resonators parameters and the expected theoretical values is reported. With achieved quality factor Q ≈ 2.5 × 10⁵, these cavities show resonant peaks as narrow as few MHz, comparable with the typical Doppler linewidth of THz molecular transitions and slightly broader than the free-running QCL emission spectrum. The effects of the optical feedback from one cavity to the QCL are examined by using the other cavity as a frequency reference.

© 2015 Optical Society of America

Abstract-Terahertz photodetectors based on tapered semiconductor nanowires

L. Romeo¹, D. Coquillat², E. Husanu¹, D. Ercolani¹, A. Tredicucci³, F. Beltram¹, L. Sorba¹, W. Knap² and M. S. Vitiello^1,a)
 HIDE AFFILIATIONS
1 NEST, Scuola Normale Superiore and CNR—Istituto Nanoscienze, Piazza San Silvestro 12, I-56127 Pisa, Italy
2 Laboratoire Charles Coulomb, UMR 5221 CNRS-Universite' Montpellier 2, 34095 Montpellier, France
3 Dipartimento di Fisica, Università di Pisa, Largo Pontecorvo 3 and NEST, CNR - Istituto Nanoscienze, 56127 Pisa, Italy
a) miriam.vitiello@sns.it
Appl. Phys. Lett. 105, 231112 (2014); http://dx.doi.org/10.1063/1.4903473

http://scitation.aip.org/content/aip/journal/apl/105/23/10.1063/1.4903473?showFTTab=true&containerItemId=content/aip/journal/apl

We report on the demonstration of Terahertz (THz) broadband detectors based on field effect transistors exploiting tapered semiconductor nanowires. The intrinsic asymmetry provided by the nanowires geometry allows to achieve responsivity values as high as 55 V/W (2.5 mA/W) and a noise-equivalent-power of 3 × 10⁻¹⁰ W/Hz^1/2 independent of the specific gate voltage applied. The possibility to reduce the number of terminals required to the source and drain contacts only and the technological feasibility of multi-pixel arrays are promising for the realization of compact and integrated THz matrix array detection systems.

Synopsis: High-Precision Terahertz Spectroscopy

Frequency-Comb-Assisted Terahertz Quantum Cascade Laser Spectroscopy

S. Bartalini, L. Consolino, P. Cancio, P. De Natale, P. Bartolini, A. Taschin, M. De Pas, H. Beere, D. Ritchie, M. S. Vitiello, and R. Torre

Phys. Rev. X 4, 021006 (2014)

Published April 9, 2014

Trace-gas sensing with high sensitivity and precision in the terahertz regime can be important in environmental monitoring, security, and astrophysics, as well as in tests of fundamental physics. Now, as reported in Physical Review X, a research team has performed the first terahertz spectroscopic measurements using a so-called frequency comb—a technique that allows frequency measurements with extremely high accuracy. As a proof-of-principle, the team measured a rotational transition in a gas molecule (methanol) to a precision of 4 parts in one billion, 10 times better than the previous record. The result is also twice as precise as the theoretically predicted frequency, suggesting the technique could help refine theoretical models.

Saverio Bartalini of the Italian National Institute of Optics (INO-CNR) and the European Laboratory for Non-linear Spectroscopy (LENS) and his colleagues have taken a terahertz system they previously developed and used it for spectroscopy. The researchers focused near-infrared laser pulses into a nonlinear crystal to produce a terahertz comb—a single beam containing thousands of discrete and closely spaced frequencies of light. The comb is referenced to a cesium atomic clock. To provide enough intensity for spectroscopy, they “phase locked” a quantum cascade laser to one of the comb’s “teeth.” The result is an ultrastable source with which they can measure the absorption of a gas sample as they slowly vary the laser frequency. With some simple improvements, the authors believe they can further boost their measurement precision by a factor of 100. – David Ehrenstein

Abstract-Graphene field-effect transistors as room-temperature terahertz detectors

http://graphenetimes.com/2012/09/graphene-field-effect-transistors-as-room-temperature-terahertz-detectors-2/

Authors: L. Vicarelli, M. S. Vitiello, D. Coquillat, A. Lombardo, A. C. Ferrari, W. Knap, M. Polini, V. Pellegrini A. Tredicucci

The unique optoelectronic properties of graphene make it an ideal platform for a variety of photonic applications, including fast photodetectors, transparent electrodes in displays and photovoltaic modules, optical modulators, plasmonic devices, microcavities, and ultra-fast lasers. Owing to its high carrier mobility, gapless spectrum and frequency-independent absorption, graphene is a very promising material for the development of detectors and modulators operating in the terahertz region of the electromagnetic spectrum (wavelengths in the hundreds of micrometres), still severely lacking in terms of solid-state devices. Here we demonstrate terahertz detectors based on antenna-coupled graphene field-effect transistors. These exploit the nonlinear response to the oscillating radiation field at the gate electrode, with contributions of thermoelectric and photoconductive origin. We demonstrate room temperature operation at 0.3 THz, showing that our devices can already be used in realistic settings, enabling large-area, fast imaging of macroscopic samples.

Nature Materials. doi:10.1038/nmat3417

Abstract Phase-locking to a free-space terahertz comb for metrological-grade terahertz lasers

http://www.nature.com/ncomms/journal/v3/n9/abs/ncomms2048.html

• L. Consolino,
• A. Taschin,
• P. Bartolini,
• S. Bartalini,
• P. Cancio,
• A. Tredicucci,
• H. E. Beere,
• D. A. Ritchie,
• R. Torre,
• M. S. Vitiello
• & P. De Natale

Optical frequency comb synthesizers have represented a revolutionary approach to frequency metrology, providing a grid of frequency references for any laser emitting within their spectral coverage. Extending the metrological features of optical frequency comb synthesizers to the terahertz domain would be a major breakthrough, due to the widespread range of accessible strategic applications and the availability of stable, high-power and widely tunable sources such as quantum cascade lasers. Here we demonstrate phase-locking of a 2.5 THz quantum cascade laser to a free-space comb, generated in a LiNbO₃ waveguide and covering the 0.1–6 THz frequency range. We show that even a small fraction (<100 nW) of the radiation emitted from the quantum cascade laser is sufficient to generate a beat note suitable for phase-locking to the comb, paving the way to novel metrological-grade terahertz applications, including high-resolution spectroscopy, manipulation of cold molecules, astronomy and telecommunications.

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