The development of highly sensitive, high-speed photodetectors using cost-effective, less toxic materials has attracted significant interest. This study examines CdS thin films with 0, 2, 4, and 6 wt% doping concentrations of Gadolinium (Gd) for photodiode applications. The films were deposited on glass substrates at 300°C using the low-cost nebulizer spray pyrolysis technique. X-ray diffraction (XRD) confirmed the presence of the hexagonal CdS phase in all samples, with the 6 wt% Gd-doped films exhibiting the highest crystallinity. Morphological analysis revealed densely packed grains in the 6 wt% Gd-doped film, while the undoped sample showed smaller grain sizes. Gd doping enhanced optical absorption, reducing the bandgap from 2.57 eV in undoped CdS to 2.37 eV in the 6 wt% Gd-doped film. Current-voltage measurement showed that the 6 wt% Gd-doped film demonstrated the best performance, with a responsivity (R) of 27.4 mA/W, a detectivity (D*) of 9.2 × 10 ¹ ⁰ Jones, and an external quantum efficiency (EQE) of 108.2 %. These results indicate that the 6 wt% Gd-doped CdS thin film is highly suitable for optoelectronic applications. © 2025 Elsevier B.V., All rights reserved.