2D analogue of band-bending in metal–semiconductor junctions: interior to edge-states of single-layered transition metal dichalcogenides

Abstract

Band-edges and the bandgap of liquid-exfoliated tungsten disulfide and tungsten diselenide (WS2 and WSe2) were measured via scanning tunneling spectroscopy (STS). We have observed that the edges of the dichalcogenides were metallic and the interiors were semiconducting in nature. An explicit band-bending between the semiconducting interior and the metallic edge could be observed in both the 2D transition metal dichalcogenides (TMDs). The Fermi energy pinning in the 2D materials is like conventional band-bending in metal–semiconductor junctions at the 3D scale. We have further have inferred that in order to determine the bandgap of a 2D TMD, localized STS measurements should be carried out away from the edge; in this work, we have determined that the required distance should be more than the width of the depletion region, which we measured as 3.5 and 2.0 nm for WS2 and WSe2, respectively.