Computational study of LiAlSi, LiAlGe and LiGaSi Half-Heusler alloys for opto-electronic applications

In this comprehensive investigation, the structural, elastic, electronic, optical, thermodynamic and thermoelectric properties of Lithium-based ternary semiconductors, namely LiAlGe, LiAlSi, and LiGaSi were explored. Utilizing first-principle calculations, various material properties were accurately determined . The lattice constants, bulk modulus, and equilibrium total energies were obtained revealing that the three alloys are mechanically stable and show brittle behavior. Electronic band structures and density of states calculations, employing PBE+U, unveiled band gaps of 1.32 eV, 1.55 eV, and 1.47 eV for LiAlGe, LiAlSi, and LiGaSi, respectively, suggesting their suitability for photovoltaic applications. Analysis of the absorption spectra allowed the identification of the active window of the electromagnetic spectrum for these materials. Subsequently, the materials exhibited desirable optical properties, characterized by efficient optical absorption, with the highest peaks in the visible light and ultraviolet regions of the electromagnetic spectrum, low reflectivity, and a high dielectric constant. These collective findings indicate the potential of these materials for application in the field of opto-electronics. Furthermore, calculations of thermoelectric properties disclosed figure of merit values of 0.830, 1.046, and 0.697 at 950 K for the LiGaSi, LiAlSi, and LiAlGe HH alloys, respectively, further highlighting their potential for use in thermoelectric applications.