Role of Fe incorporation in modifying the structure and properties of CuO thin films for optoelectronic devices: Experimental and theoretical studies

Nanostructured copper oxide (CuO) and iron (Fe)-doped CuO thin films were successfully prepared at a temperature of 350 °C using a facile spray pyrolysis technique. Fe concentrations ranging from 2 to 8 at. % were varied in CuO to examine the impact of Fe-doping on the structural, morphological, optical, electrical, and electronic properties of the thin films. X-ray diffraction analysis confirmed a monoclinic crystal structure with prominent orientation along the (1¯11) plane. Fe-doping led to reduced crystallite sizes (45–27 nm) and increased microstrain and dislocation density. Scanning electron microscopy revealed a transformation from densely packed rock-like nanostructures to agglomerated nanoparticles incorporating Fe. The grain size decreased, averaging 0.556–0.330 μm. Energy-dispersive x-ray analysis confirmed the elemental composition and a proportional increase in Fe content. Optical transmittance reached ∼73% in the visible-NIR range, while the bandgap showed a tunable shift, rising from 1.28 to 1.56 eV at 4 at. % Fe, and then declining to 1.40 eV with further doping. Electrical resistivity decreased significantly from 1.69 to 0.24 Ω-cm. The films exhibited p-type conductivity as the carrier concentration increases from 1.11 × 1017 to 6.77 × 1017 cm−3. The Hall coefficient and mobility decreased with Fe-doping in CuO thin films. Density functional theory results showed that Fe doping introduced Fe-3d states near the band edges, modified the bandgap, and influenced electronic transport while preserving the monoclinic structure. These experimental and theoretical findings demonstrate that Fe doping can be an effective strategy for tailoring the physical properties of CuO thin films for optoelectronic and sensing applications.