We present a comparative study of the nucleation and growth of Si quantum dots on Si3N4, SiO2 and SiOxNy substrates using SiH4, low-pressure chemical vapor deposition at low temperatures (570-610 degrees C). The samples are investigated by scanning electron microscopy, high-resolution transmission electron microscopy and spectroscopic ellipsometry. We demonstrate that the chemical nature of the surface and precisely the presence of oxygen on the surface influences the Si quantum dot density. We have obtained the highest dot density of nearly 10(12) cm(-2) on a Si3N4 surface at a deposition temperature below 600 degrees C. The influence of hydrogen, provided by SiH4, decomposition, on the Si nucleation mechanisms will be discussed.