Van der Waals Metallic Alloy Contacts for Multifunctional Devices

Two-dimensional (2D) semiconductors have shown great potential for electronic and optoelectronic applications. However, their development is limited by a large Schottky barrier at the contacts because of the strong Fermi-level pinning at the metal-semiconductor interface. Here, we demonstrate that 2D metallic Mo1−x W x Te2 alloy, bonded to the 2D semiconductor channel MoTe2 via van der Waals (vdW) force, can alleviate the Fermi-level pinning at the contacts. By using asymmetric contacts consisting of low work function Ti and high work function Mo1−x W x Te2 alloy, ambipolar transistors were created, showing superior transport for both electrons and holes. The MoTe2 transistor with asymmetric contacts is unidirectional and shows prominent rectifying behavior. Moreover, this asymmetric contact scheme breaks the mirror symmetry of the built-in potential profile within the channel, which enables the device to serve as an efficient solar cell and a sensitive photodetector with low dark current. This work uncovers the great potential of 2D metallic contacts for device applications and offers a new route toward tailoring 2D electronics and photonics in the future.