Electric field effect studies of ferroelectric 2D crystals of <i>α</i>-In₂Se₃ and MBE grown fields of γ-InSe

Both In₂Se₃ and InSe feature several structural modifications with distinct electronic properties of the material, demonstrating an interesting structure-property relationship. α-In₂Se₃ is ferroelectric while γ-InSe is a noncentrosymmetric semiconductor featuring very high electronic mobility (>1000 V/cm² s at room temperature). Both semiconductors possess a van der Waals interlayer bonding. We have explored novel ferroelectric semiconductor field effect transistors (FeSmFETs) employing 2D crystals of α-In₂Se₃ as a channel material and measured the devices from room to the liquid-helium temperatures. We observed the effect of the reorientation of the polarization by gating and also found evidence for an electric field induced metallic state in this material system. We also studied very thin films of γ-InSe grown by molecular beam epitaxy and fabricated FET devices to test whether the MBE grown film have a mobility similar to the 2D crystal obtained by mechanical exfoliation.