Heavily nitrogen-doped 4H-SiC homoepitaxial films were grown on normal p-type and porous 4H-SiC (PSC) substrates. The nitrogen doping concentration and resistivity of the epitaxial films, measured by Hall measurement, were about 10(20)-10(21) cm(-3) and 0.002-0.006 Omega cm, respectively. From X-ray analysis, it was observed that the crystallinity of the epilayer grown on porous 4H-SiC substrates is better than that grown on p-type 4H-SiC substrates. In spite of the heavy doping, the full-width at half-maximum (FWHM) value of the epitaxial film, which was grown on the porous substrate, was about 13 arcsec, proving its excellent crystal quality. In contrast, the heavily nitrogen-doped epilayer, which was grown on the normal substrate, had a FWHM value of 16.9 arcsec. High-voltage transmission electron microscope (HVTEM) and scanning electron microscope (SEM) observations made clear that the enhancement of the crystallinity was caused by stress relaxation near pore boundary and defect terminations in the porous layer. (c) 2007 Elsevier B.V. All rights reserved.