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Composition-dependent optical properties and dielectric function modeling of PECVD-grown hydrogenated amorphous silicon carbonitride thin films
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Resumo(s)
Hydrogenated amorphous silicon carbonitride (a-SiCN:H) thin films were deposited by radio-frequency plasma-enhanced chemical vapor deposition (rf-PECVD) at 150 °C using SiH4, CH4, and NH3 gas mixtures with variable flow ratios. The chemical composition and hydrogen content, determined by Rutherford backscattering and elastic recoil detection analyses, revealed Si-rich carbonitrides containing 32-52 at.% Si, 3-5 at.% C, 16-44 at.% N, and 25-30 at.% H. Atomic force microscopy confirmed smooth and uniform film surfaces with RMS roughness below 1 nm, suitable for precise optical modeling. Optical transmission spectra were analyzed using an extended Tauc-Lorentz (XTL) dispersion model capable of describing non-exponential band-tail absorption. The XTL model provided excellent agreement with experiment and allowed extraction of the real and imaginary parts of the dielectric function, including sub-gap components. The optical bandgap, derived from Tauc plots, increased linearly with the elemental N/Si ratio, reflecting enhanced Si-N bond formation and a reduction in localized electronic states. The refractive index varied between 1.77 and 2.9, showing strong dependence on composition and photon energy. These results demonstrate that rf-PECVD enables low-temperature synthesis of uniform a-SiCN:H films with controllable optical properties, suitable for optoelectronic and photonic device applications.
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Publisher Copyright: © 2026 Elsevier B.V.
Palavras-chave
A-SiCN:H thin films Dielectric function Extended Tauc-Lorentz model Optical bandgap Refractive index dispersion rf-PECVD Electronic, Optical and Magnetic Materials Atomic and Molecular Physics, and Optics Spectroscopy Physical and Theoretical Chemistry Organic Chemistry Inorganic Chemistry Electrical and Electronic Engineering