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 Mo_1-xW_xTe₂ 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 Mo_1-xW_xTe₂ 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.