Optical properties of spray-deposited tin oxide films

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Abstract
Optical properties of spray-deposited tin oxide (TO) films are studied here. Optical grade TO films were deposited using monobutyl tin chloride and dibutyl tin diacetate solutions. The refractive index and extinction coefficient, n(λ) and k(λ), respectively, and film thickness of TO films are evaluated from spectrophotometric transmittance characteristics examined in the visible and UV regions. Since the interference effects are suppressed by the optical absorption in the near-IR region, both reflectance and transmittance spectra are used to evaluate n(λ) and k(λ) values. Spray-deposited TO films are found to be an indirect band gap material exhibiting an absorption minimum at ∼1.0 μm (k ≲ 10−3), an energy gap at ∼3.7 eV. A transition from a bounded electron model to a free electron model occurs at λ ≃ 1.4 μm.