Layer-dependent Schottky contact at van der Waals interfaces: V-doped WSe2 on graphene

Abstract

Contacting two-dimensional (2D) semiconductors with van der Waals semimetals significantly reduces the contact resistance and Fermi level pinning due to defect-free interfaces. However, depending on the band alignment, a Schottky barrier remains. Here we study the evolution of the valence and conduction band edges in pristine and heavily vanadium (0.44%), i.e., p-type, doped epitaxial WSe2 on quasi-freestanding graphene (QFEG) on silicon carbide as a function of thickness. We find that with increasing number of layers the Fermi level of the doped WSe2 gets pinned at the highest dopant level for three or more monolayers. This implies a charge depletion region of about 1.6 nm. Consequently, V dopants in the first and second WSe2 layer on QFEG/SiC are ionized (negatively charged) whereas they are charge neutral beyond the second layer.