Graphene and other two-dimensional materials, such as transition metal dichalcogenides, have rapidly established themselves as intriguing building blocks for optoelectronic applications, with a strong focus on various photodetection platforms. The versatility of these material systems enables their application in areas including ultrafast and ultrasensitive detection of light in the ultraviolet, visible, infrared and terahertz frequency ranges. These detectors can be integrated with other photonic components based on the same material, as well as with silicon photonic and electronic technologies. Here, we provide an overview and evaluation of state-of-the-art photodetectors based on graphene, other two-dimensional materials, and hybrid systems based on the combination of different two-dimensional crystals or of two-dimensional crystals and other (nano)materials, such as plasmonic nanoparticles, semiconductors, quantum dots, or their integration with (silicon) waveguides.

Graphene is an attractive material for optoelectronics and photodetection applications because it offers a broad spectral bandwidth and fast response times. However, weak light absorption and the absence of a gain mechanism that can generate multiple charge carriers from one incident photon have limited the responsivity of graphene-based photodetectors to ∼10(-2) A W(-1). Here, we demonstrate a gain of ∼10(8) electrons per photon and a responsivity of ∼10(7) A W(-1) in a hybrid photodetector that consists of monolayer or bilayer graphene covered with a thin film of colloidal quantum dots. Strong and tunable light absorption in the quantum-dot layer creates electric charges that are transferred to the graphene, where they recirculate many times due to the high charge mobility of graphene and long trapped-charge lifetimes in the quantum-dot layer. The device, with a specific detectivity of 7 × 10(13) Jones, benefits from gate-tunable sensitivity and speed, spectral selectivity from the short-wavelength infrared to the visible, and compatibility with current circuit technologies.

Graphene plasmons provide a suitable alternative to noble-metal plasmons because they exhibit much larger confinement and relatively long propagation distances, with the advantage of being highly tunable via electrostatic gating. We report strong lightmatter interaction assisted by graphene plasmons, and in particular, we predict unprecedented high decay rates of quantum emitters in the proximity of a carbon sheet, large vacuum Rabi splitting and Purcell factors, and extinction cross sections exceeding the geometrical area in graphene ribbons and nanometer-sized disks. Our results provide the basis for the emerging and potentially far-reaching field of graphene plasmonics, offering an ideal platform for cavity quantum electrodynamics and supporting the possibility of single-molecule, single-plasmon devices. * To whom correspondence should be addressed Surfaces plasmons (SPs), the electromagnetic waves coupled to charge excitations at the surface of a metal, are the pillar stones of applications as varied as ultrasensitive optical biosensing, 1-3 photonic metamaterials, 4 light harvesting, 5,6 optical nano-antennas, 7 and quantum information processing. [8][9][10][11] However, even noble metals, which are widely regarded as the best available plasmonic materials, 12 are hardly tunable and exhibit large ohmic losses that limit their applicability to optical processing devices.In this context, doped graphene emerges as an alternative, unique two-dimensional plasmonic material that displays a wide range of extraordinary properties. 13 This atomically thick sheet of carbon is generating tremendous interest due to its superior electronic and mechanical properties, 14-20 which originate in part from its charge carriers of zero effective mass (the so-called Dirac fermions 18 ) that can travel for micrometers without scattering, even at room temperature. 21 Furthermore, rapid progress in growth and transfer techniques have sparked expectations for large-scale production of graphene-based devices and a wide range of potential applications such as high-frequency nanoelectronics, nanomechanics, transparent electrodes, and composite materials. 17 Recently, graphene has also been recognized as a versatile optical material for novel photonic 22 and optoelectronic applications, 23 such as solar cells, photodetectors, 24 light emitting devices, ultrafast lasers, optical sensing, 25 and metamaterials. 26 The outstanding potential of this atomic monolayer is emphasized by its remarkably high absorption 27,28 ≈ πα ≈ 2.3%, where α = e 2 /hc ≈ 1/137 is the fine-structure constant. Moreover, the linear dispersion of the Dirac fermions enables broadband applications, in which electric gating can be used to induce dramatic changes in the optical properties. 29All of these photonic and optoelectronic applications rely on the interaction of propagating far-field photons with graphene. Additionally, SPs bound to the surface of doped graphene exhibit a number of favorable properties that make graphene an attractive alternative to tr...

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

The ability to manipulate optical fields and the energy flow of light is central to modern information and communication technologies, as well as quantum information processing schemes. However, because photons do not possess charge, a way of controlling them efficiently by electrical means has so far proved elusive. A promising way to achieve electric control of light could be through plasmon polaritons—coupled excitations of photons and charge carriers—in graphene. In this two-dimensional sheet of carbon atoms, it is expected that plasmon polaritons and their associated optical fields can readily be tuned electrically by varying the graphene carrier density. Although evidence of optical graphene plasmon resonances has recently been obtained spectroscopically, no experiments so far have directly resolved propagating plasmons in real space. Here we launch and detect propagating optical plasmons in tapered graphene nanostructures using near-field scattering microscopy with infrared excitation light. We provide real-space images of plasmon fields, and find that the extracted plasmon wavelength is very short—more than 40 times smaller than the wavelength of illumination. We exploit this strong optical field confinement to turn a graphene nanostructure into a tunable resonant plasmonic cavity with extremely small mode volume. The cavity resonance is controlled in situ by gating the graphene, and in particular, complete switching on and off of the plasmon modes is demonstrated, thus paving the way towards graphene-based optical transistors. This successful alliance between nanoelectronics and nano-optics enables the development of active subwavelength-scale optics and a plethora of nano-optoelectronic devices and functionalities, such as tunable metamaterials, nanoscale optical processing, and strongly enhanced light–matter interactions for quantum devices and biosensing applications.