Prediction of MXene based 2D tunable band gap semiconductors: GW quasiparticle calculations

MXenes are a large family of layered transition metal carbide/nitride materials that possess a number of desired properties such as flexible chemical composition, high mechanical strength, and excellent structural stability. Although MXene based semiconductors have attracted considerable recent research attention in the search of novel 2D electronic materials, accurate understanding of their electronic properties has not been established. In this work, we carry out fully converged GW quasiparticle calculations for M₂CO₂ (M = Hf, Zr, and Ti) MXene based 2D semiconductors and alloys using newly developed accelerated GW methods. The quasiparticle band gaps of single-layer Hf₂CO₂, Zr₂CO₂, and Ti₂CO₂ are predicted to be 2.45, 2.13, and 1.15 eV, respectively. The narrow band gap of Ti₂CO₂ is attributed to the low energy of Ti 3d as compared with the Hf and Zr d states. Considering their chemical similarity, it is expected that Hf_2-2xTi_2xCO₂ semiconductors can be synthesized without difficulties. We show that the quasiparticle band gap of Hf_2-2xTi_2xCO₂ (0 ≤x≤ 1) semiconductor alloy can be continuously tuned from 2.45 to 1.15 eV, offering a unique 2D semiconductor with a moderate and tunable gap for future electronics applications.