Molybdenum disulfide (MoS
2), among many other atomically thin two-dimensional (2D)
materials, has attracted considerable attention over the past years, holding great promise for
future applications in next-generation logic circuit devices due to its ultrathin nature, desirable
bandgap (~ 1.8 eV), superior mobility, and excellent thermal stability. While many exciting
achievements have been reported on MoS
2-based metal oxide semiconductor field effect
transistors (MOSFETs), there are two main challenges that are blocking the further
development of such devices. Firstly, it is hard to achieve high-performance MoS
2MOSFETs,
as they are seriously limited by large contact resistance and low carrier mobility. Secondly,
fabricating p-channel MoS
2MOSFETs remains a challenging task due to...[
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Molybdenum disulfide (MoS
2), among many other atomically thin two-dimensional (2D)
materials, has attracted considerable attention over the past years, holding great promise for
future applications in next-generation logic circuit devices due to its ultrathin nature, desirable
bandgap (~ 1.8 eV), superior mobility, and excellent thermal stability. While many exciting
achievements have been reported on MoS
2-based metal oxide semiconductor field effect
transistors (MOSFETs), there are two main challenges that are blocking the further
development of such devices. Firstly, it is hard to achieve high-performance MoS
2MOSFETs,
as they are seriously limited by large contact resistance and low carrier mobility. Secondly,
fabricating p-channel MoS
2MOSFETs remains a challenging task due to severe Fermi level
pinning at the metal/ MoS
2 contacts, blocking the hole transportation at the source/drain ends.
In this work, MoS
2 n-MOSFETs on a 1-μm channel length with a high current drive have
been achieved on an ultrathin high-k dielectric (∼ZrO
2/Si). High drain current I
DS exceeding ~200 μA/μm and an on/off ratio of about ~ 10
6 have been achieved for multilayer MoS
2 n-MOSFETs on a ZrO
2/Si substrate. High extrinsic mobility ~ 69 cm
2/Vs and intrinsic mobility
~ 132 cm
2/Vs have been extracted in the fabricated devices because of the enhanced screening
effect of the high-k ZrO
2 dielectric on Coulomb impurities scattering. A low contact resistance
below 1 kΩ-μm has also been achieved, and is attributed to the strong electrostatic doping effect
on the contact region by using the ultrathin high-k dielectric. Strong gate coupling is also shown
on the ZrO
2/Si-supported MoS
2 MOSFETs, as much lower gate voltages are required and strong
drain current saturation are demonstrated compared to SiO
2 back-gated devices.
Enhancement-mode p-channel MoS
2 MOSFETs with high drive current and a suppressed
ambipolar effect have also been achieved. A reactive metal, Scandium, is used to form the
source/drain electrodes, which together with the interface dipoles contributed by ZrO
2 pin the
Fermi level near the valence band of the MoS
2, leading to a large hole current. Niobium (Nb)
dopes the MoS
2 p-type reducing the depletion region width at the contact, enhancing hole
tunneling. Furthermore, the larger barrier height at the conduction band suppresses the
ambipolar electron current at the off-state. The fabricated device shows unipolar current-voltage
characteristics with high on-current in the range of 10 μA/μm, while the ambipolar
current is at the level of 10 nA/μm.
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