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 PH3 and SiCl2H2 in H2. PH3 remarkably enhances the silicon deposition rate in the range 550-750°C in contrast to previously reported doping studies using SiH 4. Chemical concentrations as high as 2.5×1020 cm-3 with an electrical activity of 1×1020 cm -3 were obtained in layers that were free of defects by transmission electron microscopy. The doping level can be modulated between 1×10 19 and 5×1016 cm-3 indicating 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.