To grow epitaxial Si films with atomic- and electronic-level perfection,a high-temperature chemical vapor deposition (CVD) process (>1000 °C) has been generally employed. To reduce the growth temperature below600 °C but keeping a high deposition rate, other energy sources than thermal heating are required.Atmospheric pressure plasma CVD (AP-PCVD) is considered to be suitable for fabricatinghigh-quality films at high deposition rates due both to the high radical densityand to the low ion bombardment against the film surface, because the collisionfrequency among ions and neutral atoms is high. The present study focuses on thelow-temperature growth of epitaxial Si, and experimentally demonstrates thatAP-PCVD is capable of growing epitaxial Si films with high perfection applicable forsemiconductor devices. It is found that the pre-growth cleaning of the Si surface byH2 AP plasma is effective to grow high-purity Si films, and that the exposure of a film-growingsurface to AP plasma during growth is important to form particle-free and defect-free Sifilms. From the experimental results and the first-principles molecular dynamicssimulations of surface atomic reactions, it can be mentioned that both H atoms in the APplasma and high-density He atoms having thermal kinetic energy contribute to thereduction of growth temperature by supplying considerable energy to the surface.