Mechanisms of formation involved in both thin films and crystalline precipitates of silicon carbide (SiC) are studied in this Ph. D. thesis. SiC is fabricated starting from single-crystalline silicon (Si) substrates by carbonization or by ion implantation. The characterization of these structures allows to gather data and better physical and chemical understanding of these systems.The main objectives are (i) the fabrication and characterization of SiC and other interesting crystalline phases obtained from Si wafers and (ii) to demonstrate that these products are a viable way for using them as templates, compliant, seed or buffer layers in SiC or III-N overgrowth by epitaxial growth techniques. These approaches let the consecution of a crystalline quality enough to the development of devices. Indeed, their use allow a significant reduction of the high defect density present in III-N or SiC alloys compared to their quality when directly grown on Si. Therefore, long life are foreseen for electronic devices that could use these substrates. This is the limit needed for the beginning of their industrial production and commercialization.Samples studied in this work are framed inside three groups: (1) Silicon Carbide and other phases (Silicon Nitride (Si3N4) and carbon nitride (C3N4)) synthesized by Silicon ion implantation, (2) Silicon Carbide synthesized by Si carbonisation and (3) Silicon Carbide and Gallium Nitride heteroepitaxial growth on carbonized Si. All these structures are fabricated by techniques derived from classic (i) Ion Beam Induced Crystallization (IBIC), (ii) Chemical Vapour Deposition (CVD) or (iii) Molecular Beam Epitaxy (MBE). Structural characterizations are carried out mainly by (i) Scanning Electron Microscopy (SEM), (ii) Transmission Electron Microscopy (TEM), (iii) Fourier Transform Infra Red Spectrometry (FTIR) and other techniques.298 p
