Semiconducting Properties of Delaminated Titanium Nitride Ti₄N₃T_x MXene with Gate-Tunable Electrical Conductivity

MXenes have garnered significant attention due to their atomically thin two-dimensional structure with metallic electronic properties. However, it has not yet been fully achieved to discover semiconducting MXenes to implement them into gate-tunable electronics such as field-effect transistors and phototransistors. Here, a semiconducting Ti₄N₃T_x MXene synthesized by using a modified oxygen-assisted molten salt etching method under ambient conditions, is reported. The oxygen-rich synthesis environment significantly enhances the etching reaction rate and selectivity of Al from a Ti₄AlN₃ MAX phase, resulting in well-delaminated and highly crystalline Ti₄N₃T_x MXene with minimal defects and high content of F and O, which led to its improved hydrophobicity and thermal stability. Notably, the synthesized Ti₄N₃T_x MXene exhibited p-type semiconducting characteristics, including gate-tunable electrical conductivity, with a current on-off ratio of 5 × 10³ and a hole mobility of ∼0.008 cm² V^-1 s^-1 at 243 K. The semiconducting property crucial for thin-film transistor applications is evidently associated with the surface terminations and the partial substitution of oxygen in the nitrogen lattice, as corroborated by density functional theory (DFT) calculations. Furthermore, the synthesized Ti₄N₃T_x exhibits strong light absorption characteristics and photocurrent generation. These findings highlight the delaminated Ti₄N₃T_x as an emerging two-dimensional semiconducting material for potential electronic and optoelectronic applications.