Energy Barrier at Indium/Indium Selenide Nanosheet Interfaces: Implications of Metal-to-Insulator Transition for Field-Effect Transistor Modeling

The energy barrier formed at the interface between a 2D material and a bulk metal is a critical factor for determining the performance of nanoelectronic devices. While the Schottky–Mott rule is a commonly used guide to target suitable metal contacts, it fails to predict the correct band alignment at a metal/2D material interface due to the presence of surface states or a strong coupling between the 2D material and metal. We used X-ray photoemission spectroscopy, a surface-sensitive technique, to monitor the potential energy distribution at the interface between indium and indium selenide (the In/InSe interface). The shifts of the core-level peak after deposition of In were used to determine the valence band offset. In addition, temperature-dependent transport measurements were used to determine the energy barrier. Arrhenius analyses of the gate-dependent drain current confirmed the energy barrier formed at the In/InSe interface to be of ∼0.04 eV. This barrier height confirmed the good quality of the In contact to InSe. Moreover, the temperature dependence of transfer curves showed that the conductivity of InSe can be tuned from metallic to insulating by conventional SiO2 dielectric gate tuning. These findings not only provided a simple way for utilizing InSe in the applications of high-performance nanoelectronics (e.g., photosensors, high-mobility transistors, and memory devices) but also demonstrated that an InSe field-effect transistor with a SiO2 gate dielectric serves as a good platform for the study of metal to insulator transition mechanisms. The ability to tune the phase of InSe may find applications in superconductors, data storage devices, and photodetectors.