Energy Band And Work Function Engineering Of Few-layer MoS₂:First Principles Calculations

Owing to its novel structure and unique physical properties, Mo S2, a graphene-like two-dimensional material, is expected to apply in field-effect transistor, optoelectronic devices and many other areas. However, during the experimental fabrication and application process, its electrical properties are inevitable altered by some factors, e.g., the lattice mismatch strain of electrode, defects of gate dielectric material and Fermi pinning effect etc. how to obtain a high quality MoS₂ as a channel materials is an issue in the film transistor field. In this paper, based on the first principle calculation method, the work function and energy band of MoS₂ with different thickness is studied, and effect of sulfur atom vacancy and oxygen atom impurities on its work function and energy band, as well as the energy band alignment of MoS₂（0001） / Au（111） vacancy structure are studied. The main content are listed as follows,（1） Firstly, the effects of different strain states on band gap are studied. Band gap of monolayer MoS₂ decreases rapidly with the increasing of applied compressive and tensile strain, as same as few-layer MoS₂. The relationship of different layers/interlayer distance and the MoS₂ energy band/work function are explored, i.e., with the increase of layers, the band gap decreases, and close to the bulk band gap. Work function is of the local ordering, but its trend increases more obvious in balance distance. Further, we obtain a simply structure parameters-band gap expression for few-layer MoS₂ film, which could be used as a guidance to control the band gap of MoS₂ s by using suitable structure parameters.（2） Secondly, the energy band and the electronic work function of the sulfur atom vacancy concentration in a monolayer MoS₂ are calculated, and the energy band and the change of the electronic work function vs different concentration vacancy are analyzed. We find that vacancy of the system could leads the decrease of band gap. In the special position, the doping of sulfur and oxygen atoms could make the MoS₂ exhibit metallic properties. As for the work function, it increases（due to the substrate bias） with the increase of the sulfur atom concentration, but oxygen concentration make its slight fluctuation. These results provide a theoretical guidance for the application of MoS₂ precision devices.（3）Thirdly, by establishing the atomic model of Au/MoS₂ stacking structure, the influence of different sulfur atom vacancy on the energy band properties and effective work function is studied. The effective work function increases with the increase of the concentration of sulfur atom. Moreover, the introduction of sulfur atoms can reduce the Schottky barrier rapidly, which makes the Au/MoS₂ stack appear ohmic contact type.