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

Abstract

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 hetero-bilayers by stacking α- and δ-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 (Δy) equivalent to ~3.75 Å, whereas, the vdW coupling between the constituting monolayers has been realized for Δy as large as 7 Å. The weakening of the vdW interactions driven by the increase in Δy has resulted in the widening of the energy bandgaps. The α-type vdW bilayers exhibited indirect bandgap whereas nearly direct bandgap has been realized for δ-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 ~105 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.