Abstract
In this work, monolayer molybdenum disulfide (MoS2) nanosheets, obtained via chemical vapor deposition onto SiO2/Si substrates, are exploited to fabricate field-effect transistors with n-type conduction, high on/off ratio, steep subthreshold slope and good mobility. We study their electric characteristics from 10−6 Torr to atmospheric air pressure. We show that the threshold voltage of the transistor increases with the growing pressure. Moreover, Schottky metal contacts in monolayer molybdenum disulfide (MoS2) field-effect transistors (FETs) are investigated under electron beam irradiation conditions. It is shown that the exposure of Ti/Au source/drain electrodes to an electron beam reduces the contact resistance and improves the transistor performance. It is shown that e-beam irradiation lowers the Schottky barrier at the contacts due to thermally induced atom diffusion and interfacial reactions. The study demonstrates that electron beam irradiation can be effectively used for contact improvement though local annealing. It is also demonstrated that the application of an external field by a metallic nanotip induces a field emission current, which can be modulated by the voltage applied to the Si substrate back-gate. Such a finding, that we attribute to gate-bias lowering of the MoS2 electron affinity, enables a new field-effect transistor based on field emission.
Highlights
Transition metal dichalcogenides (TMDs) have attracted a lot of attention in the past decades due to their several promising properties for electronic and optoelectronic applications
We note that the effect of air pressure on the channel conductance, which could result in the dramatic transformation of n-type to p-type conduction when passing from high vacuum to atmospheric pressure, has been reported for other 2D TMDs materials such as WSe2 or PdSe2 (REF)
We have found that the threshold voltage of the transistor increases monotonously with the air pressure
Summary
Transition metal dichalcogenides (TMDs) have attracted a lot of attention in the past decades due to their several promising properties for electronic and optoelectronic applications. TMDs consist of a “sandwich” structure (layer) with a transition-metal sheet located in between two chalcogen sheets and possess unique properties such as energy bandgap tunable by the number of layers (from 0 to about 2.2 eV), good mobility up to few hundreds cm2V−1s−1, photoluminescence, broadband light adsorption, pristine interfaces without out-of-plane dangling bonds that allows the fabrication of hetero-structures, exceptional flexibility, thermal stability in air, and high scalability for device fabrication [1,2,3,4] They can be produced by mechanical or liquid exfoliation, chemical vapor deposition (CVD), molecular beam epitaxy, pulsed laser deposition, etc. MoS2 field effect transistors (FETs) have recently become very popular as alternatives to graphene FETs [15,16,17,18,20,21,22] for generation electronics based on 2D-materials [23,24,25,26,27,28,29]
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