Li-based ternary semiconductors: Probing electronic, mechanical, optical, and transport nature from first principles study

This study investigates the optoelectronic, mechanical, and transport properties of LiGaSe₂ and LiGaTe₂ chalcogenides crystallizing in the orthorhombic Pna2₁ phase, employing density functional theory (DFT) with TB-mBJ and WC-GGA functionals. Electronic band structure analysis validates LiGaSe₂ as a direct-band-gap and LiGaTe₂ as an indirect-band-gap semiconductor. Te substitution causes more orbital hybridization and band flattening near the Fermi level. A significant Se/Te-p and Ga-p contributions in the valence band and Ga-s/p activity in the conduction band, while Li is electrostatically passive. LiGaTe₂ has raised visible-region absorption, a greater static dielectric constant, and noticeable plasmonic activity, while LiGaSe₂ provides larger high-energy transitions suitable for UV optics. Mechanical study shows that both compounds are elastically stable and ductile. LiGaTe₂ has greater bulk, shear, and Young's moduli, indicating higher stiffness, anisotropy, and Cauchy pressure. At 700 K, LiGaTe₂ outperforms LiGaSe₂ in Seebeck coefficient and dimensionless figure of merit because of larger energy filtering and lower electronic thermal conductivity, despite lower electrical conductivity. These results indicate that chalcogen substitution influences interatomic interactions, electrical dispersions, and phonon scattering, providing a mechanism for controlling multifunctional features. LiGaTe₂ is a promising semiconductor for thermoelectric and optoelectronic applications, whereas LiGaSe₂ is still useful in UV and electronic transport-sensitive areas.