22 research outputs found
Growth and applications of two-dimensional single crystals
Two-dimensional (2D) materials have received extensive research attentions
over the past two decades due to their intriguing physical properties (such as
the ultrahigh mobility and strong light-matter interaction at atomic thickness)
and a broad range of potential applications (especially in the fields of
electronics and optoelectronics). The growth of single-crystal 2D materials is
the prerequisite to realize 2D-based high-performance applications. In this
review, we aim to provide an in-depth analysis of the state-of-the-art
technology for the growth and applications of 2D materials, with particular
emphasis on single crystals. We first summarize the major growth strategies for
monolayer 2D single crystals. Following that, we discuss the growth of
multilayer single crystals, including the control of thickness, stacking
sequence, and heterostructure composition. Then we highlight the exploration of
2D single crystals in electronic and optoelectronic devices. Finally, a
perspective is given to outline the research opportunities and the remaining
challenges in this field
Scalable High-Mobility Graphene/hBN Heterostructures
Graphene-hexagonal boron nitride (hBN) scalable heterostructures are pivotal
for the development of graphene-based high-tech applications. In this work, we
demonstrate the realization of high-quality graphene-hBN heterostructures
entirely obtained with scalable approaches. hBN continuous films were grown via
ion beam-assisted physical vapor deposition directly on commercially available
and used as receiving substrates for graphene single-crystal
matrixes grown by chemical vapor deposition on copper. The structural,
chemical, and electronic properties of the heterostructure were investigated by
atomic force microscopy, Raman spectroscopy, and electrical transport
measurements. We demonstrate graphene carrier mobilities exceeding in ambient conditions, 30% higher than those directly measured on
. We prove the scalability of our approach by measuring more than
100 transfer length method devices over a centimeter scale, which present an
average carrier mobility of . The reported high-quality
all-scalable heterostructures are of relevance for the development of
graphene-based high-performing electronic and optoelectronic applications
Phonon-mediated room-temperature quantum Hall transport in graphene
The quantum Hall (QH) effect in two-dimensional electron systems (2DESs) is
conventionally observed at liquid-helium temperatures, where lattice vibrations
are strongly suppressed and bulk carrier scattering is dominated by disorder.
However, due to large Landau level (LL) separation (~2000 K at B = 30 T),
graphene can support the QH effect up to room temperature (RT), concomitant
with a non-negligible population of acoustic phonons with a wave-vector
commensurate to the inverse electronic magnetic length. Here, we demonstrate
that graphene encapsulated in hexagonal boron nitride (hBN) realizes a novel
transport regime, where dissipation in the QH phase is governed predominantly
by electron-phonon scattering. Investigating thermally-activated transport at
filling factor 2 up to RT in an ensemble of back-gated devices, we show that
the high B-field behaviour correlates with their zero B-field transport
mobility. By this means, we extend the well-accepted notion of phonon-limited
resistivity in ultra-clean graphene to a hitherto unexplored high-field realm.Comment: 17 pages, 4 figures. Supplementary information available at
https://doi.org/10.1038/s41467-023-35986-
Ultrafast, Zero-Bias, Graphene Photodetectors with Polymeric Gate Dielectric on Passive Photonic Waveguides.
We report compact, scalable, high-performance, waveguide integrated graphene-based photodetectors (GPDs) for telecom and datacom applications, not affected by dark current. To exploit the photothermoelectric (PTE) effect, our devices rely on a graphene/polymer/graphene stack with static top split gates. The polymeric dielectric, poly(vinyl alcohol) (PVA), allows us to preserve graphene quality and to generate a controllable p-n junction. Both graphene layers are fabricated using aligned single-crystal graphene arrays grown by chemical vapor deposition. The use of PVA yields a low charge inhomogeneity ∼8 × 1010 cm-2 at the charge neutrality point, and a large Seebeck coefficient ∼140 μV K-1, enhancing the PTE effect. Our devices are the fastest GPDs operating with zero dark current, showing a flat frequency response up to 67 GHz without roll-off. This performance is achieved on a passive, low-cost, photonic platform, and does not rely on nanoscale plasmonic structures. This, combined with scalability and ease of integration, makes our GPDs a promising building block for next-generation optical communication devices