Development of Eu-doped CdS photodetectors with enhanced photodetection performance

Eu-doped CdS nanostructured thin films with varying Eu concentrations (0, 2, 4, 6, 8, and 10 wt%) were synthesized using the spray pyrolysis technique. The fabricated films were systematically evaluated for their structural, optical, electrical, and photodetection characteristics. X-ray diffraction confirmed the formation of polycrystalline hexagonal CdS with preferred growth along the (101) plane, with crystallite sizes in the range of 11-14 nm. Raman spectra supported the structural observations by revealing the characteristic 1LO and 2LO phonon modes at 299 cm^{- 1} and 601 cm^{- 1}. AFM imaging (2D/3D) further confirmed the formation of grain clusters across all samples. Optical measurements indicated transmittance values of 55-85% and direct band gaps between 2.42 and 2.44 eV. Photoconductivity studies under dark and illuminated conditions in the 297-350 K range revealed a decrease in activation energy with increasing Eu content, indicating enhanced carrier generation and transport. Transient photoconductivity showed that carrier and differential lifetimes increased with Eu incorporation. The photocurrent improved significantly with Eu doping, with the 10 wt% Eu-doped film exhibiting approximately a 22-fold enhancement compared to undoped CdS. Photodetectors fabricated using these films demonstrated enhanced visible-light photodetection performance. The device based on the 10 wt% Eu-doped CdS film exhibited rapid rise (0.20-0.38 s) and decay (0.36-0.46 s) times, along with substantial improvements in responsivity (8.71 A/W), external quantum efficiency (1710%), and specific detectivity (4 × 10¹³ Jones). These findings indicate that Eu-doped CdS thin films offer strong potential for high-performance photosensing applications.