The effects of substrate temperature (25 less than or equal to T-s less than or equal to 437 degrees C) on the structure and properties of reactive pulsed laser deposited (RPLD) carbon nitride (CNx) films prepared at a fixed nitrogen ambient pressure of 200 mTorr were investigated. The structure and composition of the films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and IR absorption, while the electrical and optical properties were studied by photothermal deflection spectroscopy, optical transmission and electrical conductivity measurements. The results show that the films contain graphitic rings, in which some of the carbon atoms are replaced by nitrogen atoms. The atomic fraction of nitrogen drops from 0.27 to 0.13 as T-s increases from 25 to 437 degrees C, indicating that the incorporation of nitrogen is hindered by a rise in T-s. As a consequence, the optical band gap and the width of electron tail states become narrower, and the room temperature electrical conductivity increases greatly such that the properties of the films deposited at high temperature approach those of graphite.