The optical and electrical properties of undoped and low doped polycrystalline silicon films deposited by LPCVD technique are analysed. Photothermal deflexion spectroscopy, and electrical conductivity in the temperature range 50-475 K are used. The effect of low phosphorus doping on the density of defects, electrical parameters and hopping conduction are examined and interpreted in conjunction with the passivation of defects by the introduction of phosphorus atoms. The density of states at the Fermi level is also calculated.