Abstract
The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides. Here we report the determination of band offsets in the heterostructures of transition metal dichalcogenides by using microbeam X-ray photoelectron spectroscopy and scanning tunnelling microscopy/spectroscopy. We determine a type-II alignment between MoS2 and WSe2 with a valence band offset value of 0.83 eV and a conduction band offset of 0.76 eV. First-principles calculations show that in this heterostructure with dissimilar chalcogen atoms, the electronic structures of WSe2 and MoS2 are well retained in their respective layers due to a weak interlayer coupling. Moreover, a valence band offset of 0.94 eV is obtained from density functional theory, consistent with the experimental determination.
Highlights
The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides
The valence bands primarily comprise of sp orbitals, with a smooth density of states (DOS)
It has been shown recently that with the presence of a thin native oxide (B2 nm) layer the photoemission measurement can be carried out without the charging effect, but the oxide is thick enough to ensure that the Si band structure is suppressed so the valence band structure detected is only from SL-TMDs21
Summary
The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides. In conventional semiconductor heterojunctions (HJs), one commonly used technique to determine the valence band offset (VBO) is XPS14–17 This method relies on finding the core-level alignment of two constituent semiconductors across the HJ. With additional information on the core-level position relative to the valence band maximum (VBM) measured separately for individual semiconductors, the VBM alignment across the HJ can be determined. The application of this technique to TMD HJs, faces two technical challenges. By using microbeam X-ray photoelectron spectroscopy (m-XPS) where the photon spot can be focused down to sub-microns (spot size B100 nm), we are able to measure the core-level alignment across the TMD HJs at the local scale. The first-principles calculations are performed to elucidate the interlayer interaction
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