We report on the growth of in situ boron doped Si and Si1-xGex epitaxial layers at 510 degrees C by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition. Boron concentration increases with B2H6 partial pressure. The boron concentration decreases as microwave power increases in Si epilayers and as Ge fraction increases in Si1-xGex epilayers. Enhanced ion bombardment at these conditions promotes the desorption of boron hydride in the growth surface. No growth rate change is observed in the Si epilayer with B2H6 partial pressure. However, a significant growth rate decrease is observed for the Si1-xGex epilayer with B2H6 partial pressure.