This paper presents results of investigations about the influence of Hydrogen (introduced by annealing or plasma implantation), and Helium (ion implantation followed by a proper annealing for creating nanocavities) on the electrical properties of 4H-SiC n-type epitaxial samples. First, 4HSiC epitaxial layers were hydrogenated either by annealing under H2 ambient or by a RF plasma treatment. This last process took place before or after the deposition of Schottky contacts. Two different annealing temperatures were imposed (300°C and 400°C), as well as two plasma hydrogen doses for the same low energy. An improvement of electrical characteristics (25 % increasing of the minority carrier diffusion length, lowering of ideality factor, better switching characteristic) is detected for samples annealed at 400°C. The treatment of 4H-SiC surface in hydrogen plasma through Ni metal also increases the diffusion length, but not sufficiently to have an effect on I-V characteristics. A second set of 4H-SiC epitaxial layers were secondly implanted with He+ ions at two distinct temperatures. An annealing at 1700°C during 30 minutes under argon atmosphere was then carried out. C-V measurements revealed the presence of a high charge density zone around the nanocavities, containing fixed negative charges, opposite in sign to the donor atoms.