First-principles investigation of Mg-based MgAl2X4 (X = S, Se) spinels for optoelectronic and energy harvesting applications

Abstract

Magnesium-based chalcogenides have emerged as promising candidates for optoelectronic and energy harvesting devices. In this study, we investigate the structural, electronic, optical, elastic, and thermoelectric properties of MgAl₂X₄ (X = S, Se) using density functional theory (DFT). Structural optimization confirms thermodynamic stability with negative formation energies of − 0.994 eV (MgAl₂S₄) and − 1.359 eV (MgAl₂Se₄). The modified Becke-Johnson (mBJ) potential reveals direct band gaps of 2.8 eV for MgAl₂S₄ and 1.9 eV for MgAl₂Se₄, suitable for optoelectronic applications. Optical analysis shows strong absorption in the visible–UV range, with absorption coefficients of \(\sim\) 50 × 10⁴ cm⁻¹ for MgAl₂S₄ and \(\sim\) 60 × 10⁴ cm⁻¹ for MgAl₂Se₄. Elastic constants confirm mechanical stability and ductile behavior, while thermoelectric analysis reveals high Seebeck coefficients and figure of merit (zT) values of 0.96 and 0.95 for MgAl₂S₄ and MgAl₂Se₄, respectively. The combination of favorable electronic, optical, and thermoelectric properties underscores the potential of MgAl₂X₄ chalcogenides for advanced applications in photovoltaics and thermoelectric devices.

Graphical abstract

Figure (a) shows the absorption coefficient, while Figure (b) presents the figure of merit at 300 K, highlighting the suitability of the materials for optoelectronic and thermoelectric applications.