Physical properties of novel Tin-chalcogenides heterostructures: A first-principles study

In recent years, the van der Waals (vdW) Heterostructures (HTSs) are broadly studied for their capabilities to modulate the performance of two-dimensional (2D) materials. Herein, we constructed four types of vdW HTSs by vertically stacking the α-polytype and δ-polytype of single-layered SnS and SnSe. The constructed HTSs have been designated as HTS-I (SnS(α)/SnS(δ)), HTS-II (SnSe(α)/SnSe(δ)), HTS-III (SnS(α)/SnSe(δ)), and HTS-IV (SnSe(α)/SnS(δ)) and their physical properties are systematically explored by the first-principles approach. The electron density mapping revealed that the monolayers constituting these HTSs are stacked by vdW coupling which persists for interlayer distance (Δy) up to ∼7 Å. However, these tin-chalcogenide-based HTSs demonstrated the highest formation energies (E_f) and binding energies (E_b) for Δy = ∼3.75 Å. The electronic structure calculations revealed them as semiconductors of indirect bandgaps of magnitude 1.22, 1.28, 1.06, and 1.22 eV recorded for HTS-I, HTS-II, HTS-III, and HTS-IV, respectively. They exhibited type-II (staggered) band alignment where the valence band maximum occurs in the δ-type of monolayer and the conduction band minimum is located in α-type of monolayers that causes the splitting of the photo-generated electron-hole pairs at the interface. Therefore, the staggering gap and large density of states observed near the bandgap edges have triggered a significantly improved optical absorption in these HTSs compared to freestanding monolayers. Moreover, the transparent nature of these HTSs has been recognized against incident light of energy less than 5 eV. These predictions illustrate the development of vdW HTSs as an effective approach to improve the functionalities of 2D materials for advanced technological applications.