Computational Study of Ohmic Contact at Bilayer InSe-Metal Interfaces: Implications for Field-Effect Transistors

Two-dimensional (2D) semiconducting InSe has received great attention due to its high mobility. Compared with its monolayer, bilayer (BL) InSe has a more appropriate band gap as the channel of field-effect transistors (FETs). As a prerequisite to constructing a high-performance FET based on BL InSe, it is necessary to find suitable metal electrodes to form Ohmic contact to InSe. Here, we systematically study the properties of the interfaces between BL InSe and a train of frequently used metallic electrodes (Ag, Sc, Cu Au, Pd, and Pt) for the first time based on density functional theory (DFT) and the ab initio quantum transport simulations (QTS). No vertical Schottky barrier exists at all the interfaces between the metals and the upper contact InSe layer due to the band hybridization (Sc, Pd, and Pt) or the occupation of the Fermi level in the conduction band (Ag, Au, and Cu). However, the band structures projected to the bottom noncontact InSe layer are preserved well for all the metals, and vertical Schottky barriers are formed for all the metal contacts at the interfaces between the contact and the noncontact InSe layers. According to the QTS, Sc, Au, Pt, and Pd form electron Schottky barrier contacts with BL InSe in the lateral direction, and the corresponding Schottky barrier heights (SBHs) for electron are 0.16, 0.20, 0.33, and 0.38 eV, respectively. Importantly, Cu and Ag both form desirable lateral Ohmic contacts with BL InSe. Our work presents guidance for the implementation of high-performance BL InSe FETs.