Heavily phosphorus and boron doped hydrogenated amorphous silicon films were deposited in the temperature range 50 to 300 °C. Concentrations of P, B and H, IR spectra and room temperature conductivity have been measured. When the deposition temperature is raised from 50 to 300 °C the concentration of P increases, while the concentration of B decreases. The dark conductivity of both P and B doped films decreases dramatically when the deposition temperature is lowered. We interpret these results on the basis of assumptions concerning the microstructure of the deposited films, and especially the variation of this structure with deposition temperature.