Published in Nanoscale 8, 8947 (2016).
Tuning Electronic Transport in Epitaxial Graphene-based van der Waals Heterostructures
Yu-Chuan Lin,1 Jun Li,b Sergio C. de La Barrera,2 Sarah M. Eichfeld,1 Yifan Nie,3 Patrick C. Mende,2 Kyeongjae Cho,3 Randall M. Feenstra,2 and Joshua A. Robinson1
1Department of Materials Science and Engineering and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA 16802 USA
2Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA
3Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA
Abstract
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, the 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 (EGFH) compared to WSe2 grown on partially hydrogenated epitaxial graphene (EGPH) . 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-EGFH displays ohmic behavior at small biases due to a large hole density in the WSe2, whereas WSe2-EGPH forms a schottky barrier junction.
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