The investigation on the structural, electronic and optical properties of wide band gap semiconductor material Bi24M2O40 (M = Si, Ge, As, P)

The mechanical, optical, electrical and thermal properties of Bi₂₄M₂O₄₀ (M = Si, Ge, As, P) are calculated by using the first-principles calculations based on density functional. The results show that Bi₂₄Si₂O₄₀ has the highest elastic constant C₁₁ (195.27), strong crush resistance on the A-axis, the largest bulk modulus (111.9GPa) and shear modulus (60.1GPa), the greatest crush resistance and the strongest shear deformation resistance. Bi₂₄As₂O₄₀ has the highest hardness (9.0GPa). According to Pugh’s rule, Bi₂₄Si₂O₄₀ and Bi₂₄Ge₂O₄₀ are inherently ductile, while Bi₂₄P₂O₄₀ and Bi₂₄As₂O₄₀ are inherently brittle. The structural energy band curves show that Bi₂₄M₂O₄₀ (M = Si, Ge, As, P) belongs to the direct band gap semiconductor. The static dielectric functions of Bi₂₄Si₂O₄₀, Bi₂₄Ge₂O₄₀, Bi₂₄P₂O₄₀ and Bi₂₄As₂O₄₀ are 4.37, 4.45, 4.47 and 4.49, respectively. The maximum absorption coefficient of Bi₂₄P₂O₄₀ is greater than that of the other three crystals and its maximum absorption coefficient is close to 2 × 10⁵cm⁻¹. In the far ultraviolet region, Bi₂₄Ge₂O₄₀ has the highest reflectivity and can be used in semiconductor shading devices. In the range of 0–10 eV, the dielectric function curves of E_X direction and E_Z direction have high anisotropy. If it is greater than 10 eV, it is isotropic. Bi₂₄P₂O₄₀ has the best thermodynamic stability at high temperatures. The order of phase stability of four semiconductor is Bi₂₄As₂O₄₀ > Bi₂₄P₂O₄₀ > Bi₂₄Ge₂O₄₀ > Bi₂₄Si₂O₄₀.