Schottky barrier engineering via adsorbing gases at the sulfur vacancies in the metal-MoS₂ interface

Sulfur vacancies (S-vacancies) are common in monolayer MoS₂ (mMoS₂). Finding an effective way to control rather than abolish the effect of S-vacancies on contact properties is vital for the application of mMoS₂. Here, we propose the adsorption of gases to passivate the S-vacancies in Pt-mMoS₂ interfaces. Results demonstrate that gases are stably and preferentially adsorbed at S-vacancies. The n-type Schottky barriers of Pt-mMoS₂ interfaces are reduced significantly upon the adsorption electron-donor gases, especially Cl₂. The n-type transport character of the Pt-mMoS₂ interface can be changed to p-type by the adsorption of electron-acceptor gases. As the adsorption concentration increases, both n- and p-type Schottky barriers are further reduced, and the lowest n- and p-type Schottky barriers are 0.36 and 0 eV, respectively. Note that the variations in Schottky barriers are independent of the oxidizing ability of gases but relative to the average number of valence electrons per gas atom. Analysis demonstrates that although gases at S-vacancies cannot cause gap states to vanish, and can even enhance Fermi level pinning, they modulate charge redistribution and the potential step at the interface region. Moreover, with increasing adsorption concentration, the valence band maximum of mMoS₂ shows the opposite variation tendency to that of the potential step. Our results suggest that adsorption of gases is an effective way to passivate S-vacancies to modulate the transport properties of Pt-mMoS₂ interfaces.