Designing Electrical Contacts to ${\mathrm{MoS}}_2$ Monolayers: A Computational Study

Studying the reason why single-layer molybdenum disulfide (${\mathrm{MoS}}_2$) appears to fall short of its promising potential in flexible nanoelectronics, we find that the nature of contacts plays a more important role than the semiconductor itself. In order to understand the nature of ${\mathrm{MoS}}_2/\mathrm{metal}$ contacts, we perform ab initio density functional theory calculations for the geometry, bonding, and electronic structure of the contact region. We find that the most common contact metal (Au) is rather inefficient for electron injection into single-layer ${\mathrm{MoS}}_2$ and propose Ti as a representative example of suitable alternative electrode materials.

Figure 1

Side view of the relaxed contact region at the interface between ${\mathrm{MoS}}_2$ and the (a) Au(111) and (b) Ti(0001) surface. (c) Binding energy $E$ per interface metal atom as a function of the separation $d$ between ${\mathrm{MoS}}_2$ and the Ti(0001) and Au(111) surface.

Figure 2

Partial electronic density of Mo and S states, which are relevant to bonding and charge injection, in (a) the single-layer ${\mathrm{MoS}}_2$, (b) the ${\mathrm{MoS}}_2/\mathrm{Au}$ system, and (c) the ${\mathrm{MoS}}_2/\mathrm{Ti}$ system. Only a narrow energy region around the Fermi level $E_F$ is shown.

Figure 3

Electronic structure at the interface between ${\mathrm{MoS}}_2$ and (a)–(c) Au and (d)–(f) Ti. Contour plots of the charge density ${\rho }_l$ associated with states in the energy range $E_F-0.1\mathrm{eV}<E<E_F+0.1\mathrm{eV}$ in planes normal to the interface in (a) ${\mathrm{MoS}}_2/\mathrm{Au}$ and (d) ${\mathrm{MoS}}_2/\mathrm{Ti}$. Average value of $⟨{\rho }_l⟩(z)$ in planes parallel to the interface of (b) ${\mathrm{MoS}}_2/\mathrm{Au}$ and (e) ${\mathrm{MoS}}_2/\mathrm{Ti}$. Average electrostatic potential $⟨V_l⟩(z)$ in planes normal to the interface in (c) ${\mathrm{MoS}}_2/\mathrm{Au}$ and (f) ${\mathrm{MoS}}_2/\mathrm{Ti}$. The dotted line in the panels indicates the location of the sulfur layer closest to the metal and the dashed line the position of the topmost metal layer.