Titanium trisulfide monolayer : Theoretical prediction of a new direct-gap semiconductor with high and anisotropic carrier mobility

A new two-dimensional (2D) layered material, namely, titanium trisulfide (TiS₃) monolayer, is predicted to possess novel electronic properties. Ab initio calculations show that the perfect TiS₃ monolayer is a direct-gap semiconductor with a bandgap of 1.02 eV, close to that of bulk silicon, and with high carrier mobility. More remarkably, the in-plane electron mobility of the 2D TiS₃ is highly anisotropic, amounting to about 10 000 cm² V^-1 s^-1 in the b direction, which is higher than that of the MoS₂ monolayer, whereas the hole mobility is about two orders of magnitude lower. Furthermore, TiS₃ possesses lower cleavage energy than graphite, suggesting easy exfoliation for TiS₃. Both dynamical and thermal stability of the TiS₃ monolayer is examined by phonon-spectrum calculation and Born-Oppenheimer molecular dynamics simulation. The desired electronic properties render the TiS₃ monolayer a promising 2D atomic-layer material for applications in future nanoelectronics. New semiconductor: A titanium trisulfide monolayer is predicted to be a direct-gap semiconductor with ultrahigh electron mobility (≈10⁴ cm² V^-1 s^-1), which is higher than that of MoS₂ and phosphorene. The monolayer can be exfoliated from its bulk phase due to the lower exfoliation energy compared to graphite.