Fowler-Nordheim tunneling through WSe₂ vertical junctions

Van der Waals (vdW) materials consisting of 2D atomic layers have attracted lots of interest in the future electronic applications thanks to their superior electrical, optical and mechanical properties. Due to their weak interlayer coupling across physical vdW gaps, vertical charge transport through these vdW layered materials is fundamentally different from in-plane transport behaviors. In this study, we investigate detailed vertical charge transport mechanisms, especially in the regime of Fowler-Nordheim (FN) tunneling, through vertical WSe₂ junctions while controlling WSe₂-layer thickness from a monolayer to multilayers with a single atomic-thick resolution. We implement a simple but reliable device structure, graphite/WSe₂/graphite vertical heterojunctions, fabricated on a h-BN/SiO₂/Si substrate by mechanical transfer technique. We observe vertical charge transport through WSe₂ layers is governed by the FN tunneling even for a monolayer WSe₂ when the vertical junctions are applied by sufficiently high electric fields. Moreover, we find out that FN tunneling characteristics can be used for identifying not only the layer number but also characterizing key material properties of layered vdW materials such as effective mass and quasiparticle energy gap.