9 research outputs found
Hopping conduction in p-type MoS2 near the critical regime of the metal-insulator transition
We report on temperature-dependent charge and magneto transport of chemically doped MoS2, p-type molybdenum disulfide degenerately doped with niobium (MoS2: Nb). The temperature dependence of the electrical resistivity is characterized by a power law, rho(T) similar to T-0.25, which indicates that the system resides within the critical regime of the metal-insulator (M-I) transition. By applying high magnetic field (similar to 7 T), we observed a 20% increase in the resistivity at 2K. The positive magnetoresistance shows that charge transport in this system is governed by the Mott-like three-dimensional variable range hopping (VRH) at low temperatures. According to relationship between magnetic-field and temperature dependencies of VRH resistivity, we extracted a characteristic localization length of 19.8 nm for MoS2: Nb on the insulating side of the M-I transition
LOW-TEMPERATURE OHMIC CONTACT TO MONOLAYER MOS2 BY VAN DER WAALS BONDED CO/H-BN ELECTRODES
Monolayer MoS2, among many other transition metal dichalcogenides, holds great promise for future applications in nanoelectronics and optoelectronics due to its ultrathin nature, flexibility, sizable band gap, and unique spin-valley coupled physics. However, careful study of these properties at low temperature has been hindered by an inability to achieve lowerature Ohmic contacts to monolayer MoS2, particularly at low carrier densities. In this work, we report a new contact scheme that utilizes cobalt (Co) with a monolayer of hexagonal boron nitride (h-BN) that has the following two functions: modifies the work function of Co and acts as a tunneling barrier. We measure a flat-band Schottky barrier of 16 meV, which makes thin tunnel barriers upon doping the channels, and thus achieve low-T contact resistance of 3 kÎ.μm at a carrier density of 5.3 × 1012/cm2. This further allows us to observe Shubnikov-de Haas oscillations in monolayer MoS2 at much lower carrier densities compared to previous work. © 2017 American Chemical Societ
Low-Temperature Ohmic Contact to Monolayer MoS<sub>2</sub> by van der Waals Bonded Co/<i>h</i>‑BN Electrodes
Monolayer MoS<sub>2</sub>, among many other transition metal dichalcogenides, holds great
promise for future applications in nanoelectronics and optoelectronics
due to its ultrathin nature, flexibility, sizable band gap, and unique
spin-valley coupled physics. However, careful study of these properties
at low temperature has been hindered by an inability to achieve low-temperature
Ohmic contacts to monolayer MoS<sub>2</sub>, particularly at low carrier
densities. In this work, we report a new contact scheme that utilizes
cobalt (Co) with a monolayer of hexagonal boron nitride (h-BN) that
has the following two functions: modifies the work function of Co
and acts as a tunneling barrier. We measure a flat-band Schottky barrier
of 16 meV, which makes thin tunnel barriers upon doping the channels,
and thus achieve low-T contact resistance of 3 kΩ.μm at
a carrier density of 5.3 × 10<sup>12</sup>/cm<sup>2</sup>. This
further allows us to observe Shubnikov–de Haas oscillations
in monolayer MoS<sub>2</sub> at much lower carrier densities compared
to previous work
Ultrafast Graphene Light Emitters
Ultrafast
electrically driven nanoscale light sources are critical
components in nanophotonics. Compound semiconductor-based light sources
for the nanophotonic platforms have been extensively investigated
over the past decades. However, monolithic ultrafast light sources
with a small footprint remain a challenge. Here, we demonstrate electrically
driven ultrafast graphene light emitters that achieve light pulse
generation with up to 10 GHz bandwidth across a broad spectral range
from the visible to the near-infrared. The fast response results from
ultrafast charge-carrier dynamics in graphene and weak electron-acoustic
phonon-mediated coupling between the electronic and lattice degrees
of freedom. We also find that encapsulating graphene with hexagonal
boron nitride (hBN) layers strongly modifies the emission spectrum
by changing the local optical density of states, thus providing up
to 460% enhancement compared to the gray-body thermal radiation for
a broad peak centered at 720 nm. Furthermore, the hBN encapsulation
layers permit stable and bright visible thermal radiation with electronic
temperatures up to 2000 K under ambient conditions as well as efficient
ultrafast electronic cooling via near-field coupling to hybrid polaritonic
modes under electrical excitation. These high-speed graphene light
emitters provide a promising path for on-chip light sources for optical
communications and other optoelectronic applications