Intriguing electronic properties of two-dimensional MoS₂/TM₂CO₂ (TM = Ti, Zr, or Hf) hetero-bilayers: type-II semiconductors with tunable band gaps

Two-dimensional (2D) transition metal compound (TMC) monolayers, as well as their van der Waals heterostructures with unique properties, are fundamentally and technologically intriguing. Here, heterostructures consisting of a MoS₂ monolayer and TM₂CO₂ (TM = Ti, Zr or Hf) monolayers are systematically researched by means of the density functional theory (DFT). Different from semiconductor/metal contacts, MoS₂ and TM₂CO₂ monolayers are all semiconductors with band gaps ranging from 0.25–1.67 eV. According to rigorous screening of stacking patterns, MoS₂/Zr₂CO₂ is shown to be an indirect type-II semiconductor with the maximum valence and minimum conduction bands spatially separated on opposite monolayers. Simultaneously, the interface charges transfer from Zr₂CO₂ to MoS₂ results in a built-in field that separates the electrons and holes efficiently. Also, the smaller effective masses of electrons and the holes of band edges indicate the higher carrier mobility. Moreover, strain regulation can make the hetero-bilayer's character a semiconductor–semimetal–metal transition. The physical insights pave the way for the good performance of MoS₂/TM₂CO₂ in next-generation electronic devices and photocatalysts. (paper)