Interfacial Properties for a Monolayer CrS2 Contact with Metal: A Theoretical Perspective

Limited calculations show that monolayer (ML) chromium dichalcogenide (CrS2) has a direct bandgap and valley polarization but with a smaller bandgap than ML MoS2 and with distinct piezoelectric and ferromagnetic properties. It is highly desirable to determine an appropriate metal contact for novel two-dimensional (2D) CrS2-based devices. By using density functional theory (DFT), the interface between ML CrS2 and commonly used metals, including s-electron and d-electron metals, is studied systematically by evaluating the binding energy, Schottky barrier, orbital overlap, and tunneling barrier at the interfaces. The d-electron metals show higher binding energy with the ML CrS2 than the s-electron metals, which is due to the different occupancy and position of the d-band of the metals. A strong Fermi level pinning is found in the metal-CrS2 contacts. Both n-type and quasi p-type phenomena for CrS2 with respect to pristine CrS2 can be produced at the CrS2 contacts with the metals. The higher overlap states between the CrS2 and Ti result in a higher minimum electron density at the Schottky interface, suggesting that Ti is the best contact among the investigated metals for use in CrS2-based devices for efficient electron injection. The DFT results provide a guideline that is invaluable for experimentally designing novel 2D CrS2 semiconductor devices.