Investigation of structural, electronic, and optical properties of 2H-AgAlO₂ delafossite for optoelectronic applications

Abstract

Motivated by the need to identify stable oxide semiconductors with suitable electronic and optical responses for solar-energy and optoelectronic applications, the structural, electrical, and optical properties of the 2H-phase AgAlO₂ delafossite are investigated in this paper using first-principles density functional theory calculations. The calculations were performed using the FP-LAPW method within the LDA and GGA-PBE approximations to evaluate the influence of the exchange–correlation treatment. To obtain a more reliable description of the electronic band gap, additional mBJ-GGA, GGA+U, and HSE calculations were also performed. Phonon-dispersion calculations were further carried out to verify the dynamical stability of the optimized 2H phase. The main research points of this work are the validation of the optimized 2H crystal structure, the identification of the indirect semiconducting band gap, the analysis of orbital contributions near the Fermi level, and the evaluation of the anisotropic optical response. Optimized structural parameters are in good accord with the theoretical and actual results presented. The phonon spectrum shows no imaginary frequencies, confirming the dynamical stability of the investigated 2H-AgAlO₂ structure. Band structure analysis indicates that AgAlO₂ is an indirect band gap semiconductor with gaps of 0.97 eV and 1.45 eV. The corrected mBJ-GGA and HSE calculations yield larger indirect band gaps of 2.446 eV and 2.423 eV, respectively, confirming the expected underestimation of the band gap by standard LDA/GGA approaches and providing a more reliable basis for discussing the optical response. The Ag-4d, Al-3p, and O-2p orbitals provide substantial contributions, according to the density of states. Contours of charge density show mixed ionic–covalent bonding. Dielectric function, refractive index, extinction coefficient, and absorption spectra are among the optical computations that show significant anisotropy and a noticeable visible-light response. The optical analysis was expanded to include the absorption coefficient, dielectric function, refractive index, energy-loss function, and reflectivity, revealing a clear polarization-dependent response between the xx and zz components. The dielectric constants and optical band gaps agree with published values. These results clarify the relationship between the electronic structure and optical behavior of 2H-AgAlO₂. These findings demonstrate 2H-AgAlO₂'s promise for photovoltaic and optoelectronic devices, especially in light-harvesting and solar energy applications. Overall, the study provides useful theoretical guidance for the design and future experimental investigation of AgAlO₂-based optoelectronic materials.