  Unlike Si, 2-dimensional (2D) Transition Metal Dichalcogenides (TMDs) offer
atomically thin channels for carrier transport in FETs. Despite advantages like
superior gate control, steep sub-threshold swing and high carrier mobility
offered by 2D FET channels, process related challenges like lack of selective
doping techniques like implantation and CMOS compatible process for fabrication
of 2D TMD based FETs hinder the anticipated viability of 2D semiconductor
technology for future electronic applications. In this letter, we demonstrate a
process oriented approach to realize superior ambipolarity in 2D FETs based on
TMDs like Molybdenum disulfide (MoS2), Tungsten disulfide (WS2), Molybdenum
diselenide (MoSe2) and Tungsten diselenide (WSe2) by enhancing hole current by
multiple orders of magnitude in otherwise strong N-type transistors. The method
involves Hydrogen Sulfide (H2S gas) assisted contact engineering of N-type FETs
to introduce surface states that alter device behavior. Based on material
characterization and bandstructure calculations, physical insights have been
developed to understand the effect of such a contact engineering technique.
Subsequently, this technique has been demonstrated to alter device behavior by
enhancing hole conduction in originally N-type exfoliated (MoS2, WS2, MoSe2 and
WSe2) and CVD grown (MoS2) TMD samples to confirm its potential towards
enabling the feasibility of 2D semiconductor device technology.
