Enhanced photo-responsivity and detectivity by Ag₁₀Se₄₀S₃₅Sb₁₅ thin films for visible light photodetectors

The incorporation of Ag and Sb impurities into the chalcogenide matrix markedly improves its electrical and nonlinear optical properties, underscoring its suitability for optoelectronic device applications. The present study investigates Ag₁₀Se₄₀S₃₅Sb₁₅ thin films fabricated by thermal evaporation and annealed at various temperatures for use as a possible visible-light photodetector. Structural analysis reveals an annealing-induced transition from an amorphous to a crystalline phase, along with a gradual increase in crystallite size. Elemental composition is verified by Energy-Dispersive X-ray (EDX) analysis, and field-emission scanning electron microscopy (FESEM) micrographs indicate enhanced porosity upon annealing. Optical characterisation reveals that annealing leads to reduced transmittance and enhanced absorption. Significant variations in optical parameters are observed, including bandgap narrowing (2.16-1.67 eV), increased optical density and extinction coefficient, and reduced skin depth. The linear refractive index increases progressively with annealing, reflecting improved optical polarisation. Furthermore, the nonlinear optical response is markedly enhanced, with the nonlinear susceptibility rising from 0.96 × 10^-11 to 2.02 × 10^-11 esu (doubled) and the nonlinear refractive index increasing from 1.36 × 10^-10 to 2.64 × 10^-10 esu (two-fold increase). Surface wettability analysis reveals reduced hydrophobicity and increased surface energy with annealing. The responsivity increases from 7.57 × 10^-4 to 9.68 × 10^-1 A W^-1, while the detectivity improves from 5.08 × 10⁸ to 1.91 × 10¹⁰ Jones. Overall, the combined improvements in structural, optical, and photodetection properties highlight the strong potential of annealed Ag₁₀Se₄₀S₃₅Sb₁₅ films for advanced optoelectronic device applications.