Band alignment of two-dimensional metal monochalcogenides MXs (M=Ga,In; X=S,Se,Te)

Monolayer metal monochalcogenides MXs (M=Ga,In; X=S,Se,Te) form a new class of two-dimensional semiconductors with indirect band gaps, and their band alignment information is investigated via first principles calculations. The dependence of band gap, valence-band maximum, conduction band minimum, and charge transfer on the M or X element has been obtained and can be understood from the orbital analysis of the band edges. Potential applications of metal monochalcogenides to design van der Waals heterostructures and catalyse the photo-splitting reaction of water have been discussed.