Variability of band alignment between WS2 and SiO2: Intrinsic versus extrinsic contributions

Internal photoemission of electrons was used to determine the energy position of the top valence band of mono- and few-layer WS2 on an SiO2/Si substrate. It was found, contrary to density functional theory calculations, that the valence band top in WS2 shifts up in energy with respect to the conduction band minimum of SiO2 with decreasing number of monolayers. At the same time, the band alignment of WS2 with SiO2 appears to be less sensitive to the WS2 synthesis route than in the previously studied case of the MoS2/SiO2 interface, indicating less extrinsic WS2 variability.