Abstract
The low-cost and nontoxic single-layered SnS has been recently predicted as a promising material for cutting-edge nanoscale optoelectronic and photovoltaic applications beyond the graphene and phosphorene. In this article, we assess the optoelectronic properties of five derivatives of single-layered SnS (such as alpha-,beta-, gamma-, delta-, and epsilon-SnS) using first-principles calculations. While the single-layered SnS (alpha-SnS) itself is an indirect bandgap semiconductor, its derivative delta-SnS demonstrated a direct bandgap and epsilon-SnS a nearly direct bandgap which makes them promising over phosphorene. This new class of monolayers exhibits structural anisotropy along diagonal components of magnitude 0.098, 0, 0.24, 0.007, and 0.036 for alpha-SnS, beta-SnS, gamma-SnS, delta-SnS, and epsilon-SnS respectively. The large degree of in-plane anisotropy has generated different bands dispersion and effective mass of charge carriers along the 100- and 010- directions that evolve interesting effects on their optoelectronic properties. The optical spectra of the SnS monolayers have been found significantly different along the x- and y-axis. Investigations of the excitonic binding energies indicated that the designed monolayers exhibit thermally stable excitons. The onset optical absorption energies occur over a wide range of the visible part of the electromagnetic spectrum which is appealing applications in optoelectronic and photovoltaic devices. The refractive indices and reflectivity spectra have been found significantly different along x- and y-directions that may find suitable applications in optical polarizers, filters, and shields against UV radiations. The present study is believed to provide useful guidance for the applications of SnS monolayers (delta-, and epsilon-SnS in particular) in direction-dependent nanoscale optoelectronic and photovoltaic devices beyond phosphorene and graphene.