Stability, electronic, and mechanical properties of Si/Ge substitutionally doped T2CO2 (T = Zr and Hf)

The stabilities, electronic properties, and mechanical properties of Si/Ge substitutionally doped T2CO2 (T = Zr and Hf) have been investigated by a first-principles method. The mechanical stability of these systems was verified according to the Born criteria of 2D hexagonal crystals. Thermal stability of Si/Ge substitutionally doped 2 × 2 × 1 T2CO2 (T = Zr and Hf) at room temperature was assured using AIMD simulations. The substitutional doping of Si/Ge elements brings about the band gap narrowing in T2CO2. The most obvious ones are the Si/Ge substitutionally doped 2 × 2 × 1 T2CO2 (T = Zr and Hf). The GGA band gaps for Si-doped Zr2CO2, Ge-doped Zr2CO2, Si-doped Hf2CO2, and Ge-doped Hf2CO2 are direct with the gap value being only 0.026 eV, 0.040 eV, 0.008 eV, and 0.059 eV, respectively. The band gap narrowing is mainly caused by the strong covalent T-Si/Ge bond. Strains can inevitably emerge due to the existence of substrates when using layer materials. For any one of Si/Ge substitutionally doped 2 × 2 × 1 T2CO2, the electronic band gap increases as the tensile strain increases. Hence, it is possible to modulate the electronic properties of T2CO2 (T = Zr and Hf) by Si/Ge substitutional doping and applying further strain. Not so good, the doping elements Si and Ge both reduce the mechanical properties of 2 × 2 × 1 T2CO2 (T = Zr and Hf) to some extent.