Unveiling the physical properties of RbCu3MSe4 (M = Si, Ge) direct band gap semiconductors: A systematic first-principles study

The Silicon and Germanium-based quaternary chalcogenides have remarkable features including their adjustable optical properties and outstanding thermal stability. We explored the complex interplay among the structural, electronic, optical, and thermoelectric characteristics of direct band gap novel RbCu3MSe4 (M = Si, Ge) quaternary chalcogenides by employing the well-known density functional theory. Direct type of band gap at high symmetry Г-point was noticed for both materials. The predicted band gaps of RbCu3SiSe4 and RbCu3GeSe4 are 1.32 eV and 0.73 eV, respectively. Due to the large size of germanium ions compared to silicon, the Ge–Se bonds in RbCu3GeSe4 are more wide-ranging than the Si–Se bonds in RbCu3SiSe4. The complex dielectric function along with other significant optical parameters are investigated and analyzed for their probable employment for optoelectronic applications. These examined materials are suitable to be employed in thermoelectric devices as observed from substantial and outstanding thermoelectric features. The present work could establish the potential employment of these complex systems and would open the way for advanced applications in various fields and technologies.