Optoelectronic properties of van der Waals stacked homo- and hetero-bilayers of tin-monochalcogenides: A first-principles study

In recent years, the van der Walls (vdW) stacking of two-dimensional (2D) materials has been widely practiced to improve their physical properties and functionalities. In this work, we constructed vdW homo- and heterobilayers by stacking alpha- and delta-types of SnS and SnSe monolayers and investigated their physical properties from the first-principles approach. The designed vdW bilayers exhibited the highest binding energies for interlayer separation (Delta y) equivalent to similar to 3.75 angstrom, whereas, the vdW coupling between the constituting monolayers has been realized for Delta y as large as 7 angstrom. The weakening of the vdW interactions driven by the increase in Delta y has resulted in the widening of the energy bandgaps. The alpha-type vdW bilayers exhibited indirect bandgap whereas nearly direct bandgap has been realized for delta-type of vdW bilayers. The high probability of photogenerated electronic transitions in electronic structures of these homo- and hetero-bilayers has resulted in substantial optical absorption (of the order of similar to 10(5) cm(-1)). Moreover, the constructed vdW bilayers exhibited interesting optical properties and transparent behavior in the infrared, visible, and ultraviolet ranges below 5 eV. This study indicates the vdW stacking as an effective route to engineer the physical properties of 2D tin-monochalcogenides for diverse electronic, optoelectronic, and photovoltaic applications.