## 4 Conclusions  
In this work, we present a comprehensive study of the CVD process for SiC thin films using a single-source precursor, 1,3,5-trisilacyclohexane (TSCH). Our materials-engineering-driven approach targets key challenges that hinder the integration of SiC into photonic devices, both intrinsic material limitations--such as hydrogen incorporation, surface roughness, material disorder--and fabrication-related challenges, including precise thickness control, critical for integrating SiC into photonic devices. We achieved controlled deposition of SiC thin films on Si and SiO\({}_{2}\)-on-Si substrates at temperatures \(\leq\)700 \({}^{\circ}\)C, demonstrating smooth surfaces (\(\sim\)5 A RMS roughness), precise thickness, undetectable hydrogen-related bonds, and extremely low optical absorption in the telecom range. Specifically, optical analysis using spectroscopic ellipsometry and three different fitting models--Tauc-Lorentz, Cody-Lorentz, and Cauchy-Urbach--consistently confirmed low absorption (<200 cm\({}^{-1}\)) at telecom wavelengths (\(\sim\)1550 nm), high refractive indices (\(\sim\)2.7), and \(E_{04}\) optical bandgap values of \(\sim\)2.3 eV. However, we emphasize that the reported extinction coefficients and corresponding absorption values depend significantly on the SE models used and are inherently limited by the sensitivity of ellipsometry in probing extremely low \(k\) values. To this end, the trends in the SE absorption data were correlated with PLE measurements in the telecom C-band to probe absorption characteristics directly. Collectively, this work establishes a scalable and robust pathway for the hybrid and heterogeneous integration of CMOS-compatible SiC-based photonic devices, directly overcoming materials-related barriers to improved device performance. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app15158603/s1](https://www.mdpi.com/article/10.3390/app15158603/s1)]([https://www.mdpi.com/article/10.3390/app15158603/s1](https://www.mdpi.com/article/10.3390/app15158603/s1)), Figure S1: A.i. Selected area electron diffraction (SAED) patterns revealed similar results with concentric rings corresponding to the (111), (200), (220), and (311) planes of the c-SiC sample, respectively. A.ii. High-resolution transmission electron microscopy (HRTEM) yielded a d-spacing value of 2.56 A, consistent with the (111) orientation of the 3C-SiC film B. Cross-SEM images showing the high-quality SiC/Si interface and uniformity of the a- and c-SiC (polycrystalline 3C-SiC) thin films deposited at 650 \({}^{\circ}\)C. The thickness measured from the images of AD (i) and A3 annealed (ii) samples indicates a densification of \(\sim\)20% after annealing; Table S1: Fitting parameters and SE results from three different models for the sample deposited at 650 \({}^{\circ}\)C; Table S2: Fitting parameters and SE results from three different models for the sample deposited at 700 \({}^{\circ}\)C; Table S3: SE results from three different models for the reference 25 nm SiO\({}_{2}\) on Si sample; Figure S2: Raman spectrum of 650 AD (i) and 700 AD (ii), recorded using a 532 nm excitation laser (exposure time of 15 s, 15 accumulations) in a spectral range of 200-2000 cm\({}^{-1}\). For the 650 AD sample, a broad peak was observed around 1300-1500 cm\({}^{-1}\), revealing the presence of C-C bonds in the film. Conceptualization, S.G.; methodology, S.G., S.D., and A.K. ; investigation, S.D. (CVD fabrication, SE, FTIR, XPS, AFM, XRD, and HRTEM), A.K. (CVD fabrication, SE, and PLE), A.N. (AFM, SEM, and Raman), and S.G. (CVD fabrication, SE, FTIR, and PLE); writing--original draft preparation, S.D., A.K., and S.G.; writing--review and editing, S.D., A.K., and S.G.; supervision, S.G. All authors have read and agreed to the published version of the manuscript. This research was funded by Gelset, a Group Company of the Mitsubishi Chemical Group. This material is also based upon work partially supported by the National Science Foundation under Grant No. 2138174-QuIC-TAQS.