ELECTRONIC, OPTICAL, AND VIBRATIONAL PROPERTIES OF LAYERED In0.3Ga0.7Se: A DFT AND RAMAN STUDY

The electronic structure, optical response, and vibrational properties of the In 0.3Ga0.7Se crystal were investigated using first-principles density functional theory. The dielectric tensor components were calculated, enabling a detailed analysis of the refractive index, extinction coefficient, absorpti on coefficient, optical conductivity, and reflectivity for light polarized parallel and perpendicular to the optical axis. T he results identify In 0.3Ga0.7Se as a direct -gap semiconductor with a fundamental band gap of 1.91 eV, highlighting its potential fo r optoelectronic applications in the visible spectral range. To elucidate the electronic structure, atom-projected partial densities of states were analyzed, revealing the contributions of In, Ga, and Se o rbitals to the valence and conduction bands. The vi brational properties were examined through a combined theoretical and experimental approach using density -functional perturbation theory and Raman spectroscopy. A direct comparison between the calculated phonon modes and the experimental Raman spectrum all owed the assignment of five Raman -active modes at 40, 111, 180, 225, and 256 cm-1, corresponding to A ₁, B₁, E₂, and E ₁ symmetry representations. The associated atomic displacement patterns were analyzed to clarify the n ature of lattice vibrations in the mi xed-cation system. In addition, the temperature dependence of the heat capacity was calculated over the range of 0 –400 K, providing insight into the thermodynamic behavior of In 0.3Ga0.7Se. The overall agreement between the calculated phonon frequencies and experimental Raman data confirms the reliability of the first -principles approach and establishes a consistent description of the electronic, optical, vibrational, and thermodynamic properties of this non -equiatomic In–Ga–Se solid solution.