Molybdenum disulfide (MoS₂), 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 MoS₂-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 MoS₂MOSFETs, as they are seriously limited by large contact resistance and low carrier mobility. Secondly, fabricating p-channel MoS₂MOSFETs remains a challenging task due to...[ Read more ]

Molybdenum disulfide (MoS₂), 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 MoS₂-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 MoS₂MOSFETs, as they are seriously limited by large contact resistance and low carrier mobility. Secondly, fabricating p-channel MoS₂MOSFETs remains a challenging task due to severe Fermi level pinning at the metal/ MoS₂ contacts, blocking the hole transportation at the source/drain ends.

In this work, MoS₂ n-MOSFETs on a 1-μm channel length with a high current drive have been achieved on an ultrathin high-k dielectric (∼ZrO₂/Si). High drain current I_DS exceeding ~200 μA/μm and an on/off ratio of about ~ 10⁶ have been achieved for multilayer MoS₂ n-MOSFETs on a ZrO₂/Si substrate. High extrinsic mobility ~ 69 cm²/Vs and intrinsic mobility ~ 132 cm²/Vs have been extracted in the fabricated devices because of the enhanced screening effect of the high-k ZrO₂ 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 ZrO₂/Si-supported MoS₂ MOSFETs, as much lower gate voltages are required and strong drain current saturation are demonstrated compared to SiO₂ back-gated devices.

Enhancement-mode p-channel MoS₂ 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 ZrO₂ pin the Fermi level near the valence band of the MoS₂, leading to a large hole current. Niobium (Nb) dopes the MoS₂ 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.