Molybdenum disulfide (MoS2) is a transition metal dichalcogenide (TMD). Two-dimensional, single- or few-layer MoS2, is a two-dimensional semiconductor. Whereas bulk MoS2 has an indirect band gap of 1.2 eV, MoS2 monolayers have a direct 1.8 eV electronic bandgap, allowing the production of transistors and photodetectors.
Because monolayer MoS2 has a direct bandgap, it can be used to construct interband tunnel FETs, which offer lower power consumption than classical transistors.
In 2011, B. Radisavljevic and A. Kis et al. used a halfnium oxide gate dielectric to demonstrate a room-temperature single-layer MoS2 mobility of at least 200 cm2 V−1 s−1, similar to that of graphene nanoribbons, and demonstrated transistors with room-temperature current on/off ratios of 1 × 108 and ultralow standby power dissipation.
In 2015, K. Kang et al. demonstrated 3D stacked MoS2 transistors on a 4-inch quartz substrate.
In 2016, researchers demonstrated molybdenum disulfide (MoS2) transistors with a 1-nm physical gate length using a single-walled carbon nanotube as the gate electrode. Long, aligned SWCNTs grown by chemical vapor deposition were transferred onto a n + Si/SiO2 substrate (50-nm-thick SiO2), located with a scanning electron microscope (SEM), and contacted with palladium (Pd) via lithography and metallization. These steps were followed by atomic layer deposition (ALD) of high-k ZrO2 and pick-and-place dry transfer of MoS2 onto the SWCNT covered by ZrO2. Nickel (Ni) source and drain contacts were made to MoS2 to complete the device. These ultrashort devices exhibit excellent switching characteristics with near ideal subthreshold swing of ~65 millivolts per decade and an On/Off current ratio of ~106. Simulations show an effective channel length of ~3.9 nm in the Off state and ~1 nm in the On state. 
A semiconductor can absorb photons with energy larger than or equal to its bandgap. The band gap of bulk transition metal dichalcogenide (TMD) material, such as MoS2 and WS2, down to a thickness of two monolayers is still indirect. Monolayer MoS2 has a direct bandgap (1.8 eV), which would allow a high absorption coefficient and efficient electron–hole pair generation under photoexcitation in optoelectronics applications.
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