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<p>Pure and cobalt-doped CdS thin films (Co = 1–10 wt%) were synthesized via aerosol-assisted chemical vapor deposition (AACVD) at 250&#xa0;°C. Single-source xanthate precursors were used. X-ray diffraction confirmed phase-pure wurtzite CdS. Cobalt incorporation reduced the crystallite size from approximately 27&#xa0;nm (pure) to 15&#xa0;nm at 5 wt% and increased microstrain. X-ray photoelectron spectroscopy verified the presence of Cd²⁺/S²⁻ and Co in mixed Co²⁺/Co³⁺ states without secondary phases. Optical analysis revealed a slight narrowing of the direct band gap with Co doping, from approximately 2.56&#xa0;eV (pure) to 2.49–2.50&#xa0;eV (doped films). Additionally, refractive-index dispersion and Spitzer–Fan modeling indicated a decrease in the high-frequency dielectric constant with cobalt content, consistent with reduced polarizability. Steady-state PL showed bands at ~ 485, 548, and 725&#xa0;nm, all quenched with increasing Co, consistent with added non-radiative centers. Time-resolved PL (TRPL) decays were bi-exponential in the microsecond regime. At 1 wt% Co, lifetimes dropped to τ₁ ≈ 0.21 µs and τ₂≈ 1.68 µs; at higher Co, the slow component partially recovered (τ₂≈2.6–3.3 µs). The photosensing capabilities of both pure and 10 wt% cobalt-doped films were tested across temperatures from 50&#xa0;°C to 150&#xa0;°C. The Co-10 wt% film delivered the fastest dynamics near 80&#xa0;°C, with rise and decay times of approximately 1.73&#xa0;s and 1.22&#xa0;s, respectively. In contrast, the pure film exhibited a slower rise time of around 3.4&#xa0;s. Responsivity, detectivity, and sensitivity decreased with temperature due to increased dark current. Co doping by AACVD offers a simple way to tune CdS defects and optoelectronic properties for thermally robust photodetection.</p>

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Structural, optical, and photosensing properties of cobalt-doped CdS films synthesized via AACVD for high-temperature photodetector applications

  • 期刊论文

  • 发表日期：

    2025年12月1日

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  • Amal H. Alsehli,
  • Fahad Abdulaziz,
  • Ahmed A. Aboud

摘要

Pure and cobalt-doped CdS thin films (Co = 1–10 wt%) were synthesized via aerosol-assisted chemical vapor deposition (AACVD) at 250 °C. Single-source xanthate precursors were used. X-ray diffraction confirmed phase-pure wurtzite CdS. Cobalt incorporation reduced the crystallite size from approximately 27 nm (pure) to 15 nm at 5 wt% and increased microstrain. X-ray photoelectron spectroscopy verified the presence of Cd²⁺/S²⁻ and Co in mixed Co²⁺/Co³⁺ states without secondary phases. Optical analysis revealed a slight narrowing of the direct band gap with Co doping, from approximately 2.56 eV (pure) to 2.49–2.50 eV (doped films). Additionally, refractive-index dispersion and Spitzer–Fan modeling indicated a decrease in the high-frequency dielectric constant with cobalt content, consistent with reduced polarizability. Steady-state PL showed bands at ~ 485, 548, and 725 nm, all quenched with increasing Co, consistent with added non-radiative centers. Time-resolved PL (TRPL) decays were bi-exponential in the microsecond regime. At 1 wt% Co, lifetimes dropped to τ₁ ≈ 0.21 µs and τ₂≈ 1.68 µs; at higher Co, the slow component partially recovered (τ₂≈2.6–3.3 µs). The photosensing capabilities of both pure and 10 wt% cobalt-doped films were tested across temperatures from 50 °C to 150 °C. The Co-10 wt% film delivered the fastest dynamics near 80 °C, with rise and decay times of approximately 1.73 s and 1.22 s, respectively. In contrast, the pure film exhibited a slower rise time of around 3.4 s. Responsivity, detectivity, and sensitivity decreased with temperature due to increased dark current. Co doping by AACVD offers a simple way to tune CdS defects and optoelectronic properties for thermally robust photodetection.