TiS sub(3) nanoribbons: Width-independent band gap and strain-tunable electronic properties

The electronic properties, carrier mobility, and strain response of TiS sub(3) nanoribbons (TiS sub(3) NRs) are investigated by first-principles calculations. We found that the electronic properties of TiS sub(3) NRs strongly depend on the edge type (a or b). All a-TiS sub(3) NRs are metallic with a magnetic ground state, while b-TiS sub(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-TiS sub(3) NR with rough edges, where the ribbon width differs in different regions. The maximum carrier mobility of b-TiS sub(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 super(3) cm super(2) V super(-1) s super(-1). The hole mobility of the b-TiS sub(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-TiS sub(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-TiS sub(3) NRs remain unchanged, while the band gap of b-TiS sub(3) NRs is increased significantly. The robust metallic and ferromagnetic nature of a-TiS sub(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-TiS sub(3) NRs is of potential importance in many fields of nanoelectronics, such as field-effect devices, optoelectronic applications, and strain sensors.