First-principles investigations of structural parameters, electronic structures and optical spectra of 5-5-and BeO-type of ZnO1-xSx alloys

Due to the multifunctionality of the ZnO and its physical robustness, substantial research is focused on its alloying with different materials. Here, we investigate the optoelectronic properties of mutual alloying of 5-5 type and BeO type of ZnO with ZnS (such as ZnO1-xSx for x = 0, 0.25, 0.50, 0.75, and 1). By using density functional theory (DFT), calculations for the structural, electronic, and optical properties of 5-5 type and BeO type ZnO1-xSx are carried out. We have noticed that the incorporation of S atom in 5-5 type ZnO1-xSx has reduced its bandgap from 3.12 eV to 2.63 eV. On the other hand, a remarkable improvement from 2.85 eV to 3.75 eV in the bandgaps of BeO type ZnO1-xSx has been observed which makes the BeO type ZnO1-xSx more favorable for the future optoelectronic applications. Furthermore, the valence band maximum of 5-5 type ZnO1-xSx is strongly affected by the S composition, as a result, the nature of the bandgap has been transformed from direct to indirect bandgap at x = 0.50 composition. The imaginary part of the dielectric function, the onset of the absorption spectrum, and conductivity are found to experience a redshift. Whereas the static dielectric constants and static refractive indices are found to be increased with S content in both types of ZnO1-xSx alloys. Our results show that BeO type ZnO1-xSx alloys are relatively promising candidates for optoelectronic devices.