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

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 WSe2. 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 WSe2/SiO(2)interface barrier appears to be marginal at least for the selenization and molecular-beam epitaxy growth methods.