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, 4H-SiC epitaxial layers were hydrogenated either by annealing under H-2 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 degrees and 400 degrees 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 degrees 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 IN characteristics. A second set of 4H-SiC epitaxial layers were secondly implanted with He+ ions at two distinct temperatures. An annealing at 1700 degrees 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.