Spectral UV–visible photoresponse and estimated shot-noise-limited ultraviolet detectivity of an FTO/TiO₂/Co₃O₄/Pt oxide photodiode
Sensors and Actuators A: Physical, cilt.412, 2026 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 412
- Basım Tarihi: 2026
- Doi Numarası: 10.1016/j.sna.2026.118595
- Dergi Adı: Sensors and Actuators A: Physical
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Chemical Abstracts Core, Chimica, Compendex, INSPEC, Academic Search Ultimate (EBSCO), Engineering Source (EBSCO)
- Anahtar Kelimeler: Co₃O₄, EQE, Oxide photodiode, Shot-noise-limited detectivity, Spectral photoresponse, TiO₂, WG analysis
- Ankara Üniversitesi Adresli: Evet
Özet
The steady-state spectral photoresponse and temperature-dependent dark transport of an FTO/TiO₂/Co₃O₄/Pt oxide photodiode were investigated over complementary optical and electrical operating ranges. The device comprised approximately 91 nm TiO₂ and 108 nm Co₃O₄ layers with evaporated Pt top contacts and was illuminated through the glass/FTO side. Wavelength-resolved photo-I–V measurements from 300 to 700 nm were evaluated together with temperature-dependent dark I–V measurements from 300 to 180 K. At 300 nm and −4 V, the approximately 2.0 cm² beam-footprint-normalized responsivity reaches 45.8 A W⁻¹ and the external quantum efficiency (EQE) reaches 1.89 × 10⁴ %, corresponding to an apparent external gain factor of Gapp ≈ 189. The responsivity increases from approximately 8.95 × 10⁻⁴ A W⁻¹ near zero bias to 45.8 A W⁻¹ at −4 V, demonstrating a strong dependence of the steady-state external response on the applied bias. The estimated dark-current shot-noise-limited specific detectivity (D*) is 1.39 × 10 ¹ ³ Jones at 300 nm and −4 V, while inclusion of the photocurrent contribution in the shot-noise term gives a more conservative estimated D*total of 3.10 × 10 ¹ ¹ Jones. Both values are model-based shot-noise estimates rather than detectivities obtained from direct noise-spectrum measurements. Apparent optical-transition energies of approximately 3.09 eV for TiO₂ and 2.20 and 1.36 eV for Co₃O₄ provide an energy-based interpretation of the measured 300–700 nm spectral range. A qualitative electron-affinity-based model gives estimated offsets of ΔEC ≈ 0.40 eV and ΔEV ≈ 0.49 eV, corresponding to a type-II-like energy ordering. Temperature-dependent dark-transport analysis shows that a homogeneous thermionic-emission description is physically inadequate, whereas the Werner–Güttler framework provides a more consistent description of the non-ideal barrier distribution. Overall, the study combines spectral photoresponse, bias dependence and temperature-dependent dark transport within explicitly defined optical-normalization and shot-noise-model conditions.