Revealing the weak Fermi level pinning effect of 2D semiconductor/2D metal contact: A case of monolayer In2Ge2Te6 and its Janus structure In2Ge2Te3Se3

Schottky barrier height (SBH), an energy barrier exists at the contact interface between two-dimensional (2D) semiconductor and metal electrode, plays a pivotal role in realizing high device performance. However, the SBH regulation by varing the metal work function is often blocked by the Fermi level pinning (FLP) effect. Herein, based on the density functional theory calculations, we reveal a weak FLP between monolayer In2Ge2Te6 (or Janus In2Ge2Te3Se3) and a series of 2D metals with the work functions spanning around 2 eV. This weak FLP at 2D/2D interface is mainly governed by the potential step between the metal side and semiconductor side in the junctions, which can be evidenced by the good agreement between the modified SBH and the Schottky-Mott limit. In particular, the potential step and its associated interface dipole (or net dipole) presents a linear proportional relationship for In2Ge2Te6-based junctions (or Janus In2Ge2Te3Se3-based junctions) with a slope of ca. 4. The mirror symmetry breaking of Janus In2Ge2Te3Se3 leads to a weaker FLP of Se side than that of Te side owing to the synergistic effect of interface dipole and intrinsic dipole. Therefore, the dipole strength in such 2D/2D junctions can be identified as a target feature of designing low resistance contact, which provides the guidance for reducing the FLP to obtain the tunable SBH and improving the device performance.