  Two-dimensional materials have attracted tremendous attention for their
fascinating electronic, optical, chemical and mechanical properties. However,
the band gaps of most 2D materials reported are smaller than 2.0 eV, which
greatly restricted their optoelectronic applications in blue and ultraviolet
range of the spectrum. Here, we propose a new stable sulfur nitride (S3N2) 2D
crystal that is a covalent network composed solely of S-N {\sigma} bonds. S3N2
crystal is dynamically stable as confirmed by the computed phonon spectrum and
ab initio molecular dynamics simulations in the NPT ensemble. Hybrid density
functional calculations show that 2D S3N2 crystal is a wide, direct band-gap
(3.17 eV) semiconductor with good hole mobility. These fascinating electronic
properties could pave the way for its optoelectronic applications such as blue
or ultra-violet light-emitting diodes (LEDs) and photodetectors.
