  The Janus structure, by combining properties of different transition metal
dichalcogenide (TMD) monolayers in a single polar material, has attracted
increasing research interest because of their particular structure and
potential application in electronics, optoelectronics and piezoelectronics. In
this work, Janus SnSSe monolayer is predicted by means of first-principles
calculations, which exhibits dynamic and mechanical stability. By using
generalized gradient approximation (GGA) plus spin-orbit coupling (SOC), the
Janus SnSSe monolayer is found to be an indirect band-gap semiconductor, whose
gap can easily be tuned by strain. High carrier mobilities are obtained for
SnSSe monolayer, and the hole mobility is higher than the electron mobility.
For SnSSe monolayer, a uniaxial strain in the basal plane can induce both
strong in-plane and much weaker out-of-plane piezoelectric polarizations, which
reveals the potential as a piezoelectric two-dimensional (2D) material. The
high absorption coefficients in the visible light region are observed,
suggesting a potential photocatalytic application. Calculated results show that
SnSSe monolayer has very high power factor, making it a promising candidate for
thermoelectric applications. Our works reveal that the Janus SnSSe structure
can be fabricated with unique electronic, optical, piezoelectric and transport
properties, and can motivate related experimental works.
