Tuning electronic transport in epitaxial graphene-based van der Waals heterostructures

Two-dimensional tungsten diselenide (WSe₂) has been used as a component in atomically thin photovoltaic devices, field effect transistors, and tunneling diodes in tandem with graphene. In some applications it is necessary to achieve efficient charge transport across the interface of layered WSe₂-graphene, a semiconductor to semimetal junction with a van der Waals (vdW) gap. In such cases, band alignment engineering is required to ensure a low-resistance, ohmic contact. In this work, we investigate the impact of graphene electronic properties on the transport at the WSe₂-graphene interface. Electrical transport measurements reveal a lower resistance between WSe₂ and fully hydrogenated epitaxial graphene (EG_FH) compared to WSe₂ grown on partially hydrogenated epitaxial graphene (EG_PH). Using low-energy electron microscopy and reflectivity on these samples, we extract the work function difference between the WSe₂ and graphene and employ a charge transfer model to determine the WSe₂ carrier density in both cases. The results indicate that WSe₂-EG_FH displays ohmic behavior at small biases due to a large hole density in the WSe₂, whereas WSe₂-EG_PH forms a Schottky barrier junction.