Optoelectronics, mechanical and thermoelectric properties of wide-band-gap semiconductors MgXS: X= Cd, Zn in the non-magnetic rock salt phase

Abstract

Utilizing the linearized augmented plane wave method within the wien2k package, based on Density Functional Theory (DFT) calculation, we investigate the structural, mechanical, electronic, optical, and thermoelectric properties of the semiconductor compounds Mg_0.875 × _0.125S (X = Cd, Zn) in their non-magnetic rock salt structure of type (B1) and space group Fm $\underset{\_}{3}$ m (225). We calculate the structural and mechanical properties using the WC-GGA approximation, evaluate the electronic and optical properties using the TB-mBJ approximation, and determine the thermoelectric properties using the Boltztrap code.

The obtained elastic constants, Pugh ratio, and bulk modulus B (GPa) indicate that the compounds Mg_0.875 × _0.125S (X = Cd, Zn) are fragile yet mechanically stable.

Moreover, the Debye temperature θ_D (K) of binary compound MgS is high, at 772.90 K. The energy gap values for MgS, Mg_0.875Cd_0.125S, and Mg_0.875Zn_0.125S equal 4.043 eV, 3.09 eV, and 2.82 eV, respectively. When we go from binary MgS to the ternaries containing Cd and Zn respectively, The gap moves from the ultraviolet region to the visible region. The wide band gap of the compounds constitutes an advantage for their applications in optoelectronics and photovoltaics. The compounds studied exhibit an intense peak in the ultraviolet region in the spectra of the real and imaginary parts of the dielectric constant, the absorption coefficient α(ω), and the optical conductivity σ(ω), suggesting promising opportunities for optoelectronics applications. The study of thermoelectric properties of compounds has shown that they are interesting from this point of view because of the significant values of their figures of merit (ZT).