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 C-11 (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 x 10(5) cm(-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 EX direction and EZ 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.