Energy Band Alignment of Few-Monolayer WS 2 and WSe 2 with SiO 2 Using Internal Photoemission Spectroscopy

Abstract

Internal photoemission spectroscopy was used to determine the valence band top energy position in few-monolayer WS 2 and WSe 2 films directly synthesized on top of the SiO 2 insulator. It is found that in WS 2 the valence band top edge lies systematically higher (by 0.4–0.7 eV) in energy than that in WSe 2 . This unexpected trend is seen for several synthesis methods suggesting it to be the intrinsic property of these W-based layered dichalcogenides. At the same time, a change in the WS 2 synthesis method from metal sulfurization to chemical vapor deposition leads to a ≈0.3 eV barrier change indicating a non-negligible impact of interface charges or dipoles. The influence of synthesis chemistry on the WSe 2 /SiO 2 interface barrier appears to be marginal at least for the selenization and molecular-beam epitaxy growth methods.