Prediction of a two-dimensional S3N2 solid for optoelectronic applications

Abstract

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 (${\mathrm{S}}_{3}{\mathrm{N}}_{2}$) 2D crystal that is a covalent network composed solely of S-N $\ensuremath{\sigma}$ bonds. The ${\mathrm{S}}_{3}{\mathrm{N}}_{2}$ 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 ${\mathrm{S}}_{3}{\mathrm{N}}_{2}$ crystal is a wide, direct band-gap (3.92 eV) semiconductor with a small-hole effective mass. In addition, the band gap of ${\mathrm{S}}_{3}{\mathrm{N}}_{2}$ structures can be tuned by forming multilayer ${\mathrm{S}}_{3}{\mathrm{N}}_{2}$ crystals, ${\mathrm{S}}_{3}{\mathrm{N}}_{2}$ nanoribbons, and ${\mathrm{S}}_{3}{\mathrm{N}}_{2}$ nanotubes, expanding its potential applications. The anisotropic optical response of the 2D ${\mathrm{S}}_{3}{\mathrm{N}}_{2}$ crystal is revealed by GW--Bethe-Salpeter-equation calculations. The optical band gap of ${\mathrm{S}}_{3}{\mathrm{N}}_{2}$ is 2.73 eV and the exciton binding energy of ${\mathrm{S}}_{3}{\mathrm{N}}_{2}$ 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.