Résumé: Silicon carbide, SiC, polytypes exhibit properties that can vary and can be influenced by factors such as hexagonality percentage, h. The objective of this work is to determine the impact of hexagonality percentage on several elastic and acoustic properties of SiC polytypes (3C, 10H, 8H, 6H, and 4H-SiC). We have successfully formulated relations linking the elastic moduli to the energy gaps (Eg) of the SiC polytypes after an in-depth study of the elastic moduli (Young's modulus E, bulk modulus B, and shear modulus G) in relation to the energy gap Eg. Then, the influence of hexagonality percentage on the elastic properties of SiC polytypes and their acoustic velocities (longitudinal, transverse, and Rayleigh) as well as their critical angles θL, θT et θR was analyzed and discussed to obtain semi-empirical formulas in the form: F(h) = ±h +  , which implies the existence of a near-linear relation between the elastic and acostic properties of the SiC polytypes with hexagonality percentage h. We have obtained results that theoretically support the development of SiC polytypes.

Résumé: Silicon carbide (SiC), owing to its wide bandgap, high thermal conductivity, and mechanical resilience, is a strategic material for power electronics, photonics, and surface acoustic wave (SAW) devices. Its three major polytypes, cubic 3C-SiC and hexagonal 4H- and 2H-SiC, exhibit structurally distinct lattices, which directly influence their acoustic responses. This theoretical investigation presents a comparative acoustic study of 3C, 4H, and 2H SiC based on simulations performed with Scanning Acoustic Microscopy (SAM). The methodology involves calculating acoustic reflection coefficients for longitudinal, transverse, and Rayleigh waves, followed by the extraction of the Rayleigh critical angle (θR) for each polytype. Mechanical impedance contrasts are inferred from acoustic signatures (Δz), and Fourier transforms are applied to retrieve Rayleigh wave velocities (VR) from the time-domain response. The results reveal that 4H-SiC possesses the most favorable acoustic profile, supporting its widespread use in high-voltage and smart-grid electronics. 3C-SiC, though challenged by crystallographic defects, demonstrates acoustic performance suitable for integration in photonic and quantum systems. 2H-SiC, while limited in industrial use, shows niche acoustic behaviors potentially exploitable in optoelectronic sensing. By coupling SAM-based simulation with spectral analysis, this work deepens the understanding of polytypism effects on SAW propagation. It provides essential data for the design of advanced acoustic devices operating in harsh environments.

Résumé: Understanding the directional dependence of acoustic wave velocities in anisotropic crystals is essential for optimizing the performance of advanced functional materials. In this work, the influence of elastic anisotropy on the propagation of longitudinal, transverse, and Rayleigh waves in silicon carbide (SiC) polytypes with low hexagonality is investigated, including 3C, 4H, 6H, 8H, and 10H structures. Using direction-dependent elastic - t 3C-SiC exhibits a quasi-isotropic elastic behavior, whereas hexagonal polytypes show progressively stronger elastic anisotropy with increasing stacking sequence complexity. This anisotropic behavior is particularly pronounced in the basal plane. The evolution of the universal anisotropy index confirms this trend and highlights the strong correlation between crystal structure and acoustic response. These findings provide valuable insights for the design and optimization of SiC-based devices, especially for applications in surface acoustic wave (SAW) components, resonators, and MEMS sensors.