First-Principles Investigation of Electronic, Optical, and Lattice Properties of α-In2Se3

This study presents a combined experimental and theoretical investigation of the electronic and vibrational properties of α-In2Se3, employing ellipsometric measurements, Raman scattering, and ab initio lattice dynamics calculations. Ellipsometric measurements and ab initio calculations demonstrate that the α‑In2Se3 crystal behaves as an indirect-bandgap semiconductor with an approximate bandgap of 1.0 eV. Analysis of the density of states, projected onto atoms, shows that the valence band maximum primarily arises from the p-states of Se atoms, with a minor contribution from the p-states of In atoms. In contrast, the conduction band minimum mainly consists of the s-states of In atoms and the p-states of Se atoms. By comparing Raman scattering results with ab initio calculations and conducting group-theoretical analysis, we identified the phonon modes of α-In2Se3. Our study confirms that the R3m symmetry is the correct space group for the α-In2Se3 phase.