Phosphorous nitride (PN) films were deposited on indium phosphide (InP) substrates at low temperatures below 200 degrees C by photon-assisted chemical vapour deposition using PCl3, and NH3 as source gasses, and their electrical and optical properties were investigated. The electrical leakage resistance of PN films was found to depend strongly on the ratio of source gasses (PCl3/NH3). As a result, even at 100 degrees C, PN films with resistivities of about 10(9) to 10(10) Omega cm under a high electric field (1 MV cm(-1)) were obtained without post-deposition annealing by optimizing the source gas ratio. These PN films with high resistivity have also the same optical properties as those deposited at 200 degrees C.