Hexagonal CuAlO2 for advanced optoelectronics: Insights from first-principles structural, electronic and optical analysis

Abstract

In this study, we employ first-principles simulations based on density functional theory (DFT) with a Hubbard U correction (LDA +U) to investigate the structural, electronic and optical properties of delafossite CuAlO2 in its hexagonal 2H phase. Our calculations yield optimized lattice parameters in good agreement with experimental data, revealing an indirect electronic band gap of approximately 2.4 eV and an optical band gap of about 1.9 eV. The optical properties of CuAlO2-2H reveal strong anisotropy, driven by its layered delafossite structure. The dielectric function shows a dominant absorption peak at ∼4.4 eV for light polarized perpendicular to the c-axis (ϵ), attributed to O 2p → Cu 3d interband transitions, while the parallel component ( ϵ) exhibits a weaker, blue-shifted peak around 5.0-5.2 eV, linked to O 2p → Cu 3p transitions. This anisotropy results in a higher static dielectric constant (1.7 versus 1.2), enhanced optical conductivity in the perpendicular direction and strong birefringence (3.67) and linear dichroism (5.21). The absorption coefficient, extinction coefficient and reflectivity spectra confirm a pronounced absorption edge near 3.2 eV and strong UV absorption near 5 eV, with up to 21% reflectivity, underscoring the material's directional and energy-dependent optical behavior.