To date, 100-mm silicon carbide substrates as well as high power electronic devices are commercially available. Devices performance is however limited by defects. This PhD thesis focuses on the study of defects in substrates and epitaxial layers, as well as their characterization in electronic devices. Defects located in substrates and epitaxial layers are investigated by Raman spectroscopy and Raman imaging, photoluminescence and optical microscopy in order to evidence critical parameters responsible for the modification of structural and electronic properties. The acquired knowledge is re-used for the study of defects in biased SiC PiN diodes, as well as in diamond PN junctions. Coupling between Raman spectroscopy and photoemission reveal...