High concentrations of electrically active phosphorus have been grown in Si epitaxial layers at 750 °C and below in an atmospheric pressure deposition system using PH3and SiCl2H2in H2. PH3remarkably enhances the silicon deposition rate in the range 550–750 °C in contrast to previously reported doping studies using SiH4. Chemical concentrations as high as 2.5×1020 cm−3with an electrical activity of 1×1020 cm−3were obtained in layers that were free of defects by transmission electron microscopy. The doping level can be modulated between 1×1019and 5×1016 cm−3indicating that there are no complications due to dopant retention on sample or reactor wall surfaces. Emitter‐base diodes formed in the epitaxial layers exhibited ideal forward and low‐leakage reverse characteristics.