Abstract-Nanostructured epitaxial graphene for ultra-broadband optoelectronic detectors (Conference Presentation)

Abdel El Fatimy,  Luke St. Marie,  Anindya Nath, Byoung Don Kong, Anthony K. Boyd,  Rachael L. Myers-Ward,  Kevin M. Daniels,  M. Mehdi Jadidi,  Thomas E. Murphy,  D. Kurt Gaskill, Paola Barbara

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10729/1072906/Nanostructured-epitaxial-graphene-for-ultra-broadband-optoelectronic-detectors-Conference-Presentation/10.1117/12.2321313.short

Atomically thin materials like semimetallic graphene and semiconducting transition metal dichalcogenides (TMDs) are an ideal platform for ultra-thin optoelectronic devices due to their direct bandgap (for monolayer thickness) and their considerable light absorption. For devices based on semiconducting TMDs, light detection occurs by optical excitation of charge carriers above the bandgap. For gapless graphene, light absorption causes a large increase in electron temperature, because of its small electronic heat capacity and weak electron-phonon coupling, making it suitable for hot-electron detectors. Here we show that, by nanostructuring graphene into quantum dots, we can exploit quantum confinement to achieve hot-electron bolometric detection. The graphene quantum dots are patterned from epitaxial graphene on SiC, with dot diameter ranging from 30 nm to 700 nm [1]. Nanostructuring greatly increases the temperature dependence of the electrical resistance, yielding detectors with extraordinary performance (responsivities of 1 × 10^(10) V W^(−1) and electrical noise-equivalent power, ∼2 × 10^(−16) W Hz^(−1/2) at 2.5 K). We will discuss how the dynamics of the charge carriers, namely the hot-electron cooling, affects the device operation and its power dependence. These detectors work in a very broad spectral range, from terahertz through telecom to ultraviolet radiation [2], with a design that is easily scalable for detector arrays. [1] El Fatimy, A. et al. , "Epitaxial graphene quantum dots for high-performance terahertz bolometers," Nature Nanotechnology 11, 335-338 (2016). [2] El Fatimy, A. et al. , "Ultra-broadband photodetectors based on epitaxial graphene quantum dots" Nanophotonics (2018).

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UMD Researchers Make Breakthrough in Terahertz Technology

https://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=5875769655979595840

A University of Maryland (UMD) research team, in collaboration with Monash University and the United States Naval Research Laboratory, has invented a Tunable Large Area Hybrid Metal-Graphene Terahertz Detector, an innovation based upon a successful demonstration of plasmonic resonance in graphene micro-ribbons that are connected to metal electrodes, offering a critical step toward practical graphene terahertz optoelectronic devices.

Graphene, a two-dimensional lattice of pure carbon, is extremely conductive and has unique and advantageous electronic and optical properties that are ideal for a variety of applications, such as sensors, oscillators, electronic components, filters, detectors, and more. Graphene is especially useful in terahertz range, the part of electromagnetic spectrum between microwaves and infrared light, because the free electrons in the material oscillate collectively at these frequencies. The resonance frequency can be tuned by applying an electric voltage at the gate. Being able to tune the resonance frequency allows the resonator to be adjusted, making it usable in a broad range of applications.

“Terahertz technology has a wide variety of potential scientific and commercial applications, ranging from medical diagnosis and screening, manufacturing, security screening, communications, and biochemical sensing,” said Thomas Murphy, Professor of Electrical and Computer Engineering (ECE) and Director of the Institute for Research in Electronics and Applied Physics (IREAP). The invention may offer a dramatic improvement in the ability to increase the speed of short range wireless communication, cutting the amount of time needed to stream a very high quality content between devices. It may offer means ofimproved security scanning at airports.

Until now, using graphene in terahertz sensors has primarily been theoretical because graphene must touch a metal surface to read out the results or tune the sensor, and this was previously thought to inhibit the plasmonic resonance. But the team invented a new design that does not inhibit charge accumulation at the contact and allows the signal to transfer from the graphene to the metal electrical contacts much more effectively.

The research team includes Murphy; ECE graduate student Mehdi Jadidi; United States Naval Research Laboratory researcher D. Kurt Gaskill; Michael Fuhrer, Research Professor in the Department of Physics and the Center for Nanophysics and advanced-materials/” title=”View all articles about Advanced Materials here”>Advanced Materials and Professor of Physics at Monash University in Australia; Andrei Sushkov, Assistant Research Scientist in the Department of Physics and the Center for Nanophysics and advanced-materials/” title=”View all articles about Advanced Materials here”>Advanced Materials; and H. Dennis Drew, Research Professor in the Department of Physics and the Center for Nanophysics and Advanced Materials.

Electrical connection or antenna coupling to graphene is a problem that has puzzled theresearchers for many years, but the idea behind the team’s discovery originated with Jadidi.

The discovery has the potential to advance the field, and the team is excited to continue their research and further develop the technology in preparation for commercialization.

“We would be thrilled if this invention found near-term commercial applications,” said Murphy. “Perhaps the most promising short-term application would be for room-temperature tunable terahertz detectors.

The research was funded by the Office of Naval Research and National Science Foundation and was recently featured(link is external) in the American Chemical Society’s journal, Nano Letters.

The invention has been nominated by UMD’s Office of Technology Commercialization for the Invention of the Year award in the Physical Sciences category at the Celebration of Innovation and Partnerships on May 9th as part of the University of Maryland’s “30 Days of EnTERPreneurship.”

To learn more about the University of Maryland’s “30 Days of EnTERPreneurship,” visit: http://www.umd.edu/30Days/(link is external).

Abstract-Epitaxial graphene quantum dots for high-performance terahertz bolometer

• Abdel El Fatimy,
• Rachael L. Myers-Ward,
• Anthony K. Boyd,
• Kevin M. Daniels,
• D. Kurt Gaskill
• & Paola Barbara,

http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2015.303.html

Light absorption in graphene causes a large change in electron temperature due to the low electronic heat capacity and weak electron–phonon coupling^1, 2, 3. This property makes graphene a very attractive material for hot-electron bolometers in the terahertz frequency range. Unfortunately, the weak variation of electrical resistance with temperature results in limited responsivity for absorbed power. Here, we show that, due to quantum confinement, quantum dots of epitaxial graphene on SiC exhibit an extraordinarily high variation of resistance with temperature (higher than 430 MΩ K⁻¹below 6 K), leading to responsivities of 1 × 10¹⁰ V W⁻¹, a figure that is five orders of magnitude higher than other types of graphene hot-electron bolometer. The high responsivity, combined with an extremely low electrical noise-equivalent power (∼2 × 10⁻¹⁶ W Hz^−1/2 at 2.5 K), already places our bolometers well above commercial cooled bolometers. Additionally, we show that these quantum dot bolometers demonstrate good performance at temperature as high as 77 K.

Abstract-Sensitive Room-Temperature Terahertz Detection via Photothermoelectric Effect in Graphene

Xinghan Cai, Andrei B. Sushkov, Ryan J. Suess, Mohammad M. Jadidi, Greg S. Jenkins, Luke O. Nyakiti, Rachael L. Myers-Ward, Jun Yan, D. Kurt Gaskill, Thomas E. Murphy, H. Dennis Drew,Michael S. Fuhrer

(Submitted on 14 May 2013 (v1), last revised 7 Nov 2013 (this version, v2))

http://arxiv.org/abs/1305.3297

Terahertz (THz) radiation has uses from security to medicine, however sensitive room-temperature detection of THz is notoriously difficult. The hot-electron photothermoelectric effect in graphene is a promising solution: photoexcited carriers rapidly thermalize due to strong electron-electron interactions, but lose energy to the lattice more slowly. The electron temperature gradient drives electron diffusion, and asymmetry due to local gating or dissimilar contact metals produces a net current via the thermoelectric effect. Here we demonstrate a graphene thermoelectric THz photodetector with sensitivity exceeding 100 V/W at room temperature and noise equivalent power (NEP) less than 100 pW/Hz1/2, competitive with the best room-temperature THz detectors, while time-resolved measurements indicate our graphene detector is eight to nine orders of magnitude faster. A simple model of the response, including contact asymmetries (resistance, work function and Fermi-energy pinning) reproduces the qualitative features of the data, and indicates that orders-of-magnitude sensitivity improvements are possible.