金衬底调控单层二硫化钼电子性能的第一性原理研究

基于密度泛函的第一性原理研究了金衬底对单层二硫化钼电子性能的调控作用. 从结合能、能带结构、电子态密度和差分电荷密度四个方面进行了深入研究. 结合能计算确定了硫原子层在界面的排布方式, 并指出这种吸附结构并不稳定. 能带结构分析证实了金衬底与单层二硫化钼形成肖特基接触, 并出现钉扎效应. 电子态密度分析表明金衬底并没有影响硫原子和钼原子之间的共价键, 而是通过调控单层二硫化钼的电子态密度增加其导电率. 差分电荷密度分析表明单层二硫化钼的导电通道可能在界面处产生. 研究结果可对单层二硫化钼晶体管的建模和实验制备提供指导.

Tuning the electronic property of monolayer MoS2 adsorbed on metal Au substrate: a first-principles study

Using first principles calculations within density functional theory, we investigate the electronic property of a single-layer MoS₂ adsorbed on Au. All the quantities are calculated using the Vienna ab initio simulation package. Calculations are performed using the projector augmented wave method with the Perdew-Burke-Ernzerhof functional and a kinetic energy cutoff of 400 eV. The atomic plane and its neighboring image are separated by a 15 Å vacuum layer. The k-meshes for the structure relaxation and post analysis are 9×9×1 and 19×19×1, respectively. The spin-orbit coupling is considered in the calculation. The research includes the binding energy, the band structure, density of states (DOS) and electric charge difference density. Three contact modes between MoS₂ (0001) and Au (111) are considered. When the atom S layer and the atom Au layer on the contacting interface have the same structure, the minimum binding energy and distance between MoS₂ (0001) and Au(111) are 2.2 eV and 2.5 Å respectively. The minimum binding energy confirms that the absorption is unstable. The band structure demonstrates that the MoS₂-Au contact nature is of the Schottky-barrier type, and the barrier height is 0.6 eV which is bigger than MoS₂-Sc contact. By comparison with other metal contacts such as Ru(0001), Pd(111) and Ir(111), the dependence of the barrier height on the work function difference exhibits a Fermi-level pinning. But the MoS₂ is so thin that the Fermi-level pinning must be very small. Maybe there is a metal induced gap state. DOS points out that the Au substrate has no influence on the covalent bond between Mo and S. The influence of the Au substrate is that it shifts the DOS of monolayer MoS₂ left on the axis. The change of DOS results in the increases of electron concentration and electric conductivity. Other calculation points out that Ti substrate can excite more electrons. Electric charge density difference demonstrates that there are a few electric charges that transfer on the contact interface. The conducting path of monolayer MoS₂ may emerge at the interface between Au and MoS₂. In summary, the Au electrode is not the best electrode in the MoS₂ device. The Ti electrode can excite more electrons from MoS₂. The work function of Sc electrode is close to the affine of MoS₂. The Fermi energy level of graphene can be tuned by external voltage. So the Ti, Sc and graphene will be the better electrodes for MoS₂ device. Results of this study may provide a theoretical basis for single-layer MoS₂ transistor and guidance for its applications.