11 research outputs found
van der Waals Bonded Co/h-BN Contacts to Ultrathin Black Phosphorus Devices
Due to the chemical inertness of 2D hexagonal-Boron Nitride (h-BN), few
atomic-layer h-BN is often used to encapsulate air-sensitive 2D crystals such
as Black Phosphorus (BP). However, the effects of h-BN on Schottky barrier
height, doping and contact resistance are not well known. Here, we investigate
these effects by fabricating h-BN encapsulated BP transistors with cobalt (Co)
contacts. In sharp contrast to directly Co contacted p-type BP devices, we
observe strong n-type conduction upon insertion of the h-BN at the Co/BP
interface. First principles calculations show that this difference arises from
the much larger interface dipole at the Co/h-BN interface compared to the Co/BP
interface, which reduces the work function of the Co/h-BN contact. The Co/h-BN
contacts exhibit low contact resistances (~ 4.5 k-ohm), and are Schottky
barrier free. This allows us to probe high electron mobilities (4,200 cm2/Vs)
and observe insulator-metal transitions even under two-terminal measurement
geometry
Transport properties of pristine few-layer black phosphorus by van der Waals passivation in an inert atmosphere
Ultrathin black phosphorus is a two-dimensional semiconductor with a sizeable band gap. Its excellent electronic properties make it attractive for applications in transistor, logic and optoelectronic devices. However, it is also the first widely investigated two-dimensional material to undergo degradation upon exposure to ambient air. Therefore a passivation method is required to study the intrinsic material properties, understand how oxidation affects the physical properties and enable applications of phosphorene. Here we demonstrate that atomically thin graphene and hexagonal boron nitride can be used for passivation of ultrathin black phosphorus. We report that few-layer pristine black phosphorus channels passivated in an inert gas environment, without any prior exposure to air, exhibit greatly improved n-type charge transport resulting in symmetric electron and hole transconductance characteristics.B.O. acknowledges support by the National Research Foundation, Prime Minister's Office, Singapore under its Competitive Research Programme (CRP Award No. NRF-CRP9-2011-3) and the SMF-NUS Research Horizons Award 2009-Phase II. A.H.C.N. acknowledges the NRF-CRP award 'Novel 2D materials with tailored properties: beyond graphene'. The calculations were performed at the GRC computing facilities. A.Z. and D.F.C. acknowledge the NSF grant CHE-1301157. (NRF-CRP9-2011-3 - National Research Foundation, Prime Minister's Office, Singapore under its Competitive Research Programme (CRP); SMF-NUS Research Horizons Award-Phase II; NRF-CRP award 'Novel 2D materials with tailored properties: beyond graphene'; CHE-1301157 - NSF)Published versio
Transport properties of ultrathin black phosphorus on hexagonal boron nitride
10.1063/1.4913419Applied Physics Letters106
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Tuning and Persistent Switching of Graphene Plasmons on a Ferroelectric Substrate.
We characterized plasmon propagation in graphene on thin films of the high-κ dielectric PbZr0.3Ti0.7O3 (PZT). Significant modulation (up to ±75%) of the plasmon wavelength was achieved with application of ultrasmall voltages (< ±1 V) across PZT. Analysis of the observed plasmonic fringes at the graphene edge indicates that carriers in graphene on PZT behave as noninteracting Dirac Fermions approximated by a semiclassical Drude response, which may be attributed to strong dielectric screening at the graphene/PZT interface. Additionally, significant plasmon scattering occurs at the grain boundaries of PZT from topographic and/or polarization induced graphene conductivity variation in the interior of graphene, reducing the overall plasmon propagation length. Lastly, through application of 2 V across PZT, we demonstrate the capability to persistently modify the plasmonic response of graphene through transient voltage application
Tuning and Persistent Switching of Graphene Plasmons on a Ferroelectric Substrate
We characterized plasmon propagation
in graphene on thin films of the high-κ dielectric PbZr<sub>0.3</sub>Ti<sub>0.7</sub>O<sub>3</sub> (PZT). Significant modulation
(up to ±75%) of the plasmon wavelength was achieved with application
of ultrasmall voltages (< ±1 V) across PZT. Analysis of the
observed plasmonic fringes at the graphene edge indicates that carriers
in graphene on PZT behave as noninteracting Dirac Fermions approximated
by a semiclassical Drude response, which may be attributed to strong
dielectric screening at the graphene/PZT interface. Additionally,
significant plasmon scattering occurs at the grain boundaries of PZT
from topographic and/or polarization induced graphene conductivity
variation in the interior of graphene, reducing the overall plasmon
propagation length. Lastly, through application of 2 V across PZT,
we demonstrate the capability to persistently modify the plasmonic
response of graphene through transient voltage application