The electronic properties, carrier mobility, and strain response of ${\mathrm{TiS}}_3$ nanoribbons (${\mathrm{TiS}}_3$ NRs) are investigated by first-principles calculations. We found that the electronic properties of ${\mathrm{TiS}}_3$ NRs strongly depend on the edge type (a or b). All a-${\mathrm{TiS}}_3$ NRs are metallic with a magnetic ground state, while b-${\mathrm{TiS}}_3$ NRs are direct band gap semiconductors. Interestingly, the size of the band gap and the band edge position are almost independent of the ribbon width. This feature promises a constant band gap in a b-${\mathrm{TiS}}_3$ NR with rough edges, where the ribbon width differs in different regions. The maximum carrier mobility of b-${\mathrm{TiS}}_3$ NRs is calculated by using the deformation potential theory combined with the effective mass approximation and is found to be of the order ${10}^3{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$. The hole mobility of the b-${\mathrm{TiS}}_3$ NRs is one order of magnitude lower, but it is enhanced compared to the monolayer case due to the reduction in hole effective mass. The band gap and the band edge position of b-${\mathrm{TiS}}_3$ NRs are quite sensitive to applied strain. In addition we investigate the termination of ribbon edges by hydrogen atoms. Upon edge passivation, the metallic and magnetic features of a-${\mathrm{TiS}}_3$ NRs remain unchanged, while the band gap of b-${\mathrm{TiS}}_3$ NRs is increased significantly. The robust metallic and ferromagnetic nature of a-${\mathrm{TiS}}_3$ NRs is an essential feature for spintronic device applications. The direct, width-independent, and strain-tunable band gap, as well as the high carrier mobility, of b-${\mathrm{TiS}}_3$ NRs is of potential importance in many fields of nanoelectronics, such as field-effect devices, optoelectronic applications, and strain sensors.

• Received 27 April 2015

DOI:https://doi.org/10.1103/PhysRevB.92.075413