Schottky-Barrier Formation on a Covalent Semiconductor without Fermi-Level Pinning: The Metal-MoS2(0001) Interface.

Chemical interaction and Schottky-barrier formation at the metal-MoS2 interface were studied by evaporating metals Ag, Al, Au, Co, Fe, In, Mn, Pd, Rh, Ti, and V onto the 0001 basalplane surface of cleaved molybdenite, and then analyzing the interface with x-ray photoelectron spectroscopy XPS. Except for Mn, negligible changes were revealed in the Mo3d52 and S2p32 peak shapes, or widths, after deposition. The shifts in the blinding energies did not correlate with the electron configuration of the meal but rather with the metal electronegativity, and are interpreted in terms of band bending at the metal-semiconductor interface, rather than chemical reaction. Plot of both Mo and S binding energies versus metal electronegativity yield approximately linear curves with nonzero positive slopes, which provide an average index of interface behavior of S 1.28 or - 0.22. This value is considerably higher than for other covalent semiconductors, which exhibit S 0.3 due to Fermi-level pinning. The anomalous behavior of MoS2 results from the extreme inertness of the basal-plane surface and the stability of the layered crystal lattice of MoS2. The absence of chemical interaction at the interface causes the formation of a Schottky barrier exhibiting behavior that may approach the Schottky limit. This behavior for MoS20001 is compared with that of other semiconductors, and is discussed in terms of their ionicity, reactivity, and dielectric response.