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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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.

Presentation-Graphene Plasmonics and Terahertz Photonics

Tuesday, April 29, 2014 - 3:30pm

Regents 109

Dennis Drew

Department of Physics, University of Maryland

http://www.physics.georgetown.edu/colloquia/2014/4/29/graphene-plasmonics-and-terahertz-photonics

The experimental discovery of two-dimensional (2D) gated graphene in 2004 by Novoselov and Geim is a seminal event in electronic materials science, ushering in a tremendous outburst of scientific activity in the study of electronic properties of this unique two-dimensional material with a gapless Dirac electronic spectrum. The lack of a traditional bandgap makes graphene an exceptionally versatile photonic material, and the ability to dope graphene through metallic contacts and tune the carrier density through the application of a gate opens possibilities for a variety of transformative photonic devices. In particular highly doped graphene has recently been recognized as a powerful plasmonic material that combines many important properties at terahertz (THz) frequencies with the ability of being electrically tunable. Terahertz radiation has uses from security to medicine. Currently, however, THz technology is notoriously underdeveloped. Graphene plasmonics has promise of filling in this conspicuous gap in the electromagnetic spectrum with a robust and radically new technology. Recently, sensitive room temperature THz detectors have been demonstrated that operate on a photo-thermo-electric principle with response times of 10s of femtoseconds. THz absorption in a graphene element raises the temperature of the graphene carriers, which then diffuse to the contacts made of dissimilar metals and produces a photo voltage proportional to the Seebeck coefficient of the graphene. A source of THz radiation based on this photo-thermo-electric effect also looks promising. A graphene element is used as an optical mixer of near IR to generate THz plasmons which are then coupled to free space radiation by an antenna. A review of graphene and these THz developments will be described.

Host: 

 Paola Barbara

Discussion Leader: 

 Paola Barbara

Terahertz radiation cools quantum dot sensors

http://physics.georgetown.edu/news/2012/6/6/terahertz-radiation-cools-quantum-dot-sensors

Several emerging applications of terahertz radiation, including chemical characterization of materials, communication, medical imaging and security screening, have stimulated intense research to access this region of the electromagnetic spectrum, where availability of sources and detectors is quite limited. In an upcoming issue of Nano Letters, Georgetown University scientists Dr. Mohamed Rinzan and Prof. Paola Barbara and their collaborators at the University of Maryland and Northwestern University report on a new, highly-sensitive detector of terahertz radiation. These detectors can determine the radiation frequency, unlike traditional detectors such as bolometers, and can easily detect femtowatts of power. By using on-chip antennas, the coupling of radiation to the detectors was dramatically increased. The work also shows a new, strikingly counterintuitive effect: exposure to radiation cools the sensors, which further improves their performance; bolometers and many other detectors are heated by exposure to radiation. These results can potentially be applied to graphene and pave the way to practical, highly sensitive terahertz spectral analyzers.