Strain-engineered robust and Schottky-barrier-free contact in 2D metal-semiconductor heterostructure

Two-dimensional (2D) semiconducting transition metal dichalcogenides, such as MoS2, have emerged as a promising channel material for nanoelectronic devices. However, MoS2/metal contacts usually exhibit poor stability and large Schottky barrier heights (SBHs), which severely limit their development for practical applications. Here, we use metallic MXene as a 2D electrode and propose to use strain to control the structural stability and Schottky barrier of the MoS2/MXene contact. By choosing the experimentally synthesized Ti3C2Tx (T = OH, F, O) as a prototype example, we systematically investigated the structural, energetic and electronic properties of MoS2/Ti3C2Tx heterostructures. Results show that MoS2/Ti3C2(OH)2 is an ohmic contact, while MoS2/Ti3C2F2 and MoS2/Ti3C2O2 exhibit an n-type Schottky contact with SBH ~0.73 eV and p-type contact with SBH ~0.33 eV, respectively. Remarkably, external tensile strain not only enhances the interlayer binding for robust contact, but also tunes the conduction band edge position of MoS2, which leads to efficient reduction of Fermi level pinning and SBHs so that Schottky-barrier-free contact (ohmic type) can be achieved. The physical origin lies in the strain mediated interplay between van der Waals and electrostatic interaction, and the large deformation potential of the conduction band edge state of MoS2. These results are generally applicable, demonstrating the great promise of combining assembly of van der Waals heterostructures with strain engineering for stable, high-performance 2D electronics.