Prediction of a two-dimensional S₃N₂ solid for optoelectronic applications

Two-dimensional materials have attracted tremendous attention for their fascinating electronic, optical, chemical, and mechanical properties. However, the band gaps of most reported two-dimensional (2D) materials are smaller than 2.0 eV, which has greatly restricted their optoelectronic applications in the blue and ultraviolet range of the spectrum. Here, we propose a stable trisulfur dinitride (S₃N₂) 2D crystal that is a covalent network composed solely of S-N σ bonds. The S₃N₂ crystal is dynamically, thermally, and chemically stable, as confirmed by the computed phonon spectrum and ab initio molecular dynamics simulations. GW calculations show that the S₃N₂ crystal is a wide, direct band-gap (3.92 eV) semiconductor with a small-hole effective mass. In addition, the band gap of S3N2 structures can be tuned by forming multilayer S₃N₂ crystals, S₃N₂ nanoribbons, and S₃N₂ nanotubes, expanding its potential applications. The anisotropic optical response of the 2D S₃N₂ crystal is revealed by GW-Bethe-Salpeter-equation calculations. The optical band gap of S₃N₂ is 2.73 eV and the exciton binding energy of S₃N₂ is 1.19 eV, showing a strong excitonic effect. Our result not only marks the prediction of a 2D crystal composed of nitrogen and sulfur, but also underpins potential innovations in 2D electronics and optoelectronics. © 2018 American Physical Society.