Electrical Detection of the Flat Band Dispersion in Van der Waals Field-Effect Structures

The emergence of the field-effect transistor transformed contemporary technologies. Of paramount significance to the effective operation of such devices is the minimal current leakage between the source and gate electrodes. These currents have traditionally been considered detrimental, hindering the flow of electrical charge through the channel. Consequently, for more than seven decades, leakage currents were perceived as lacking any valuable insights beyond their role in improving performance and transistor design. This research delves into the examination of gate leakage currents, specifically tunneling currents, in field-effect devices utilizing thin layers of InSe channels. InSe, known for its exceptional electrical and optical properties, as well as its distinctive band structure, exhibits a flat-band dispersion at the valence band edge, which may give rise to emergent phenomena [1]. However, determining the energy position of the flat band in a field-effect device has traditionally required costly and impractical methods. Therefore, our study focuses on analyzing tunneling currents in gated structures composed of a few layers of InSe and their relationship with ambipolar transport and photoluminescence measurements. Notably, we observe a shift in tunneling mechanisms due to the presence of the van Hove singularity at the flat band. To validate our findings, we explore tunneling currents as a reliable means of determining the position of the flat band, even at room temperature. Our study offers a fresh outlook on the enduring enigma, presenting an alternative framework for comprehending leakage currents in field-effect devices.