External pressure effect on the electronic, optical and thermoelectric properties of the CdY2Ch4 (Ch = S, Se) spinel compounds: Via modified Becke-Johnson (mBJ) exchange potential

We report the results of the FP-APW + lo calculations of the structural, electronic, optical and thermo-electric properties of the CdY2Ch4 (Ch = S, Se) compounds under hydrostatic pressure effect. The calculated ground state properties agree well with the available experimental data. The investigated materials are semiconductors, with direct band gaps (Γ- Γ) of approximately 2.18 eV, 1.53 eV for CdY2S4 and CdY2Se4, respectively, using GGA-TB-mBJ approximations. Under external pressure up to 20 GPa, both compounds show a linear decrease of energy gaps against pressure. Moreover, our calculated optical spectra over photon energies ranging from 0 to 20 eV suggest that CdY2Ch4 (Ch = S, Se) spinel compounds express a strong response in the energy range between the visible light and extreme UV regions, highlighting their possible application in the optoelectronic devices. Furthermore, the calculated thermoelectric properties indicate that both the CdY2S4 and CdY2Se4 compounds show interesting thermoelectric properties.