Band structure engineering through van der Waals heterostructing superlattices oftwo-dimensionaltransition metal dichalcogenides

The indirect-to-direct band-gap transition in transition metal dichalcogenides (TMDCs) from bulk to monolayer, accompanying with other unique properties of two-dimensional materials, has endowed them great potential in optoelectronic devices. The easy transferability and feasible epitaxial growth pave a promising way to further tune the optical properties by constructing van der Waals heterostructures. Here, we performed a systematic high-throughput first-principles study of electronic structure and optical properties of the layer-by-layer stacking TMDCs heterostructing superlattices, with the configuration space of [(MX2)(n)-(M ' X '(2))(10-n)] (M/M ' = Cr, Mo, W; X/X ' = S, Se, Te;n= 0-10). Our calculations involving long-range dispersive interaction show that the indirect-to-direct band-gap transition or even semiconductor-to-metal transition can be realized by changing component compositions of superlattices. Further analysis indicates that the indirect-to-direct band-gap transition can be ascribed to the in-plane strain induced by lattice mismatch. The semiconductor-to-metal transition may be attributed to the band offset among different components that is modified by the in-plane strain. The superlattices with direct band-gap show quite weak band-gap optical transition because of the spacial separation of the electronic states involved. In general, the layers stacking-order of superlattices results in a small up to 0.2eV band gap fluctuation because of the built-in potential. Our results provide useful guidance for engineering band structure and optical properties in TMDCs heterostructing superlattices.