High-Field Electron Transport and High Saturation Velocity in Multilayer Indium Selenide Transistors

Creating a high-frequency electron system demands a high saturation velocity (υ_sat). Herein, we report the high-field transport properties of multilayer van der Waals (vdW) indium selenide (InSe). The InSe is on a hexagonal boron nitride substrate and encapsulated by a thin, noncontinuous In layer, resulting in an impressive electron mobility reaching 2600 cm²/(V s) at room temperature. The high-mobility InSe achieves υ_sat exceeding 2 × 10⁷ cm/s, which is superior to those of other gapped vdW semiconductors, and exhibits a 50-60% improvement in υ_sat when cooled to 80 K. The temperature dependence of υ_sat suggests an optical phonon energy (ℏω_op) for InSe in the range of 23-27 meV, previously reported values for InSe. It is also notable that the measured υ_sat values exceed what is expected according to the optical phonon emission model due to weak electron-phonon scattering. The superior υ_sat of our InSe, despite its relatively small ℏω_op, reveals its potential for high-frequency electronics, including applications to control cryogenic quantum computers in close proximity.