The Novel Two-Dimensional van der Waals Crystal InSe and its Magnetic Doping

Abstract

This thesis focusses on the electronic properties of the novel two dimensional (2D) van der Waals (vdW) crystal InSe. It examines the integration of InSe in graphene-based field effect transistors (FETs) and the incorporation of transition metals in InSe to create new magnetic materials. InSe is employed in graphene-based FETs as an electrically and optically active capping layer to “modulation-dope” and photosensitise an adjacent graphene layer. This leads to a “giant” quantum Hall (QH) plateau at a filling factor v = 2 in the magnetoresistance of graphene that persists over a wide range of magnetic fields. Furthermore, the optical excitation of the FETs changes the resistance of the graphene layer. The sign of the Hall voltage and of the v = 2 QH plateau persists over a wide range of temperatures of up to T ~ 200K and can be controlled by an appropriate combination of gate voltages and optical illumination. These phenomena involve the charge transfer at the InSe/graphene interface, offering opportunities for optoelectronics and quantum metrology. Also, we studied a new hybrid material system, which comprises InSe and ferromagnetic Fe-islands. We observed that unlike many traditional semiconductors, the electronic properties of pristine InSe are largely preserved after the incorporation of Fe. Also, this system exhibits ferromagnetic resonances and a large uniaxial magnetic anisotropy at room temperature, offering opportunities for the development of functional devices that integrate magnetic and semiconducting properties within the same material system