Nanocrystalline proprieties of TiO₂ thin film deposited by ultrasonic spray

Samira Sali – Salim Kermadi – Lyes Zougar – Bouthina Benzaoui –
Nandia Saoula – Khadija Mahdid – Fatiha Aitameur – Messaoud Boumaour

   Titanium oxide (TiO₂) films have been synthesized on quartz, silicon and textured silicon substrates by chemical ultrasonic spray deposition. The textured silicon substrate was carried out using Na₂CO₃ solution. The sample surface exhibits uniform pyramids with an average height of 5 µm. In this paper, particular attention is given to the TiO₂ films prepared by spray ultrasonic system using Tetra iso-Propoxide Orthotitanate Titanium (TPOT) as a precursor. The solutions were sprayed onto substrates heated at various temperatures 350-550°C. The properties of films as a function of temperature parameter were investigated using structural and optical analysis. According to XRD, FTIR and Micro- Raman spectroscopies, the anatase phase was found and exhibits nanograins of 9 to 15 nm in size. The indirect and direct bad gap were found to increase by increasing substrate temperature due to the decreasing of nanograins size and were estimated to be around 3.28 and 3.38 eV. A transmittance higher than 80% was found. This paper reports on anti- reflection coating application of TiO₂ layers due to its good transparency and appropriate refractive index varies between 2.19-2.40 at λ = 632.8 nm as a function of temperature determined by UV–Vis–NIR spectrophotometer and Ellipsometry. To achieve optimum anti-reflection characteristics different anti-reflection designs were experimentally examined with polished and textured substrates. The average reflectance of the polished silicon used in this study is 39%, with TiO₂ it decreases to 9%. The textured surface reduces the average reflectance of silicon to be around 14% and it decreases dramatically to 5% after deposition of a single layer of TiO₂ as an anti-reflection coating. The gain in density of the short-circuit photocurrent assigned to the reduction of reflection losses up to 44% and 58% were predicted with TiO₂ single-coating in polished and textured silicon substrates respectively.

Keywords: TiO₂, Spray ultrasonic, textured silicon, anti-reflection coating

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