Vygranenko, Y.Lavareda, G.Amaral, A.Brogueira, P.2026-03-272026-03-272026-060925-3467PURE: 152078175PURE UUID: 95801e2d-07b6-4d85-8c06-aa82e9789bd1Scopus: 105028245421WOS: 001677103900001ORCID: /0000-0002-9840-6329/work/209975220http://hdl.handle.net/10362/201872Publisher Copyright: © 2026 Elsevier B.V.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.95910833engA-SiCN:H thin filmsDielectric functionExtended Tauc-Lorentz modelOptical bandgapRefractive index dispersionrf-PECVDElectronic, Optical and Magnetic MaterialsAtomic and Molecular Physics, and OpticsSpectroscopyPhysical and Theoretical ChemistryOrganic ChemistryInorganic ChemistryElectrical and Electronic Engineeringjournal article10.1016/j.optmat.2026.117903https://www.scopus.com/pages/publications/105028245421https://www.webofscience.com/wos/woscc/full-record/WOS:001677103900001