10 research outputs found
Enhanced Resonant Tunneling in Symmetric 2D Semiconductor Vertical Heterostructure Transistors
Tunneling transistors with negative differential resistance have widespread appeal for both digital and analog electronics. However, most attempts to demonstrate resonant tunneling devices, including graphene–insulator–graphene structures, have resulted in low peak-to-valley ratios, limiting their application. We theoretically demonstrate that vertical heterostructures consisting of two identical monolayer 2D transition-metal dichalcogenide semiconductor electrodes and a hexagonal boron nitride barrier result in a peak-to-valley ratio several orders of magnitude higher than the best that can be achieved using graphene electrodes. The peak-to-valley ratio is large even at coherence lengths on the order of a few nanometers, making these devices appealing for nanoscale electronics
Graphene-Molybdenum Disulfide-Graphene Tunneling Junctions with Large-Area Synthesized Materials
Tunneling devices based on vertical
heterostructures of graphene and other 2D materials can overcome the
low on–off ratios typically observed in planar graphene field-effect
transistors. This study addresses the impact of processing conditions
on two-dimensional materials in a fully integrated heterostructure
device fabrication process. In this paper, graphene-molybdenum disulfide-graphene
tunneling heterostructures were fabricated using only large-area synthesized
materials, unlike previous studies that used small exfoliated flakes.
The MoS<sub>2</sub> tunneling barrier is either synthesized on a sacrificial
substrate and transferred to the bottom-layer graphene or synthesized
directly on CVD graphene. The presence of graphene was shown to have
no impact on the quality of the grown MoS<sub>2</sub>. The thickness
uniformity of MoS<sub>2</sub> grown on graphene and SiO<sub>2</sub> was found to be 1.8 ± 0.22 nm. XPS and Raman spectroscopy are
used to show how the MoS<sub>2</sub> synthesis process introduces
defects into the graphene structure by incorporating sulfur into the
graphene. The incorporation of sulfur was shown to be greatly reduced
in the absence of molybdenum suggesting molybdenum acts as a catalyst
for sulfur incorporation. Tunneling simulations based on the Bardeen
transfer Hamiltonian were performed and compared to the experimental
tunneling results. The simulations show the use of MoS<sub>2</sub> as a tunneling barrier suppresses contributions to the tunneling
current from the conduction band. This is a result of the observed
reduction of electron conduction within the graphene sheets