Light absorption in graphene causes a significant change in electron temperature due to the low electronic heat capacity and weak electron-phonon coupling. This property makes graphene a beautiful material for hot-electron bolometers (HEB). However, along with the above advantages, a major challenge remains that, with weak electron-phonon scattering, the resistance is only weakly temperature dependent for pristine graphene. It is thus challenging to measure the electron temperature change due to incoming radiation power. In addition, thermally isolating graphene in order to achieve the small electron-phonon thermal conductance is difficult. To overcome this issue, stronger temperature dependence has been obtained either by using dual-gated bilayer graphene to create a tunable bandgap or by introducing defects to induce strong localization. Both schemes have successfully produced bolometric detection, with responsivities up to 2×105 V W−1 and a temperature coefficient for the resistance as high as 22 kΩ K−1 at 1.5 K. Here we use graphene quantum dots, where a bandgap is induced via quantum confinement and the graphene quantum dots device exhibits an extraordinarily high variation of resistance with temperature (higher than 430 MΩ K−1), leading to responsivities of 1 × 1010 V W−1.
Abdel El Fatimy, Luke St. Marie, Anindya Nath, Byoung Don Kong, Anthony Boyd, Rachael Myers-Ward, Kevin Daniels, M. Mehdi Jadidi, Thomas Murphy, D. Kurt Gaskill, Paola Barbara
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).
Nanometer size field effect transistors can operate as efficient resonant or broadband terahertz detectors, mixers, phase shifters and frequency multipliers at frequencies far beyond their fundamental cut-of frequency. This work is an
overview of some recent results concerning the low temperatures operation, linearity, and circular polarization studies of
nanometer scale field effect transistors for the detection of terahertz radiation. Also first results on graphene transistors
are discussed.
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