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Quasi-two-dimensional gallium chalcogenide heterostructures are created by transferring exfoliated few-layer GaSe onto bulk GaTe sheets. Luminescence spectroscopy measurements reveal that the light emission from underlying GaTe layers drastically increases on heterojunction regions where GaSe layers make contact with the GaTe. Density functional theory (DFT) and band offset calculations show that conduction band minimum (CBM) (valance band maximum (VBM)) values of GaSe are higher (lower) in energy compared to GaTe, forming type-I band alignment at the interface. Consequently, GaSe layers provide photo-excited electrons and holes to GaTe sheets through relatively large built-in potential at the interface, increasing overall exciton population and light emission from GaTe. Observed results are not specific to the GaSe/GaTe system but observed on GaS/GaSe heterolayers with type-I band alignment. Observed experimental findings and theoretical studies provide unique insights into interface effects across dissimilar gallium chalcogenides and offer new ways to boost optical performance by simple epitaxial coating. [ABSTRACT FROM AUTHOR]

We present in-depth measurements of the electronic band structure of the transition-metal dichalcogenides (TMDs) MoS2 and WS2 using angle-resolved photoemission spectroscopy, with focus on the energy splittings in their valence bands at the K point of the Brillouin zone. Experimental results are interpreted in terms of our parallel first-principles computations. We find that interlayer interaction only weakly contributes to the splitting in bulk WS2, resolving previous debates on its relative strength. We additionally find that across a range of TMDs, the band gap generally decreases with increasing magnitude of the valence-band splitting, molecular mass, or ratio of the out-of-plane to in-plane lattice constant. Our results provide an important reference for future studies of electronic properties of MoS2 and WS2 and their applications in spintronics and valleytronics devices. [ABSTRACT FROM AUTHOR]