We have begun a detailed study of the physical properties of Si3 N4 films deposited at low temperatures using a PECVD process based on dilution of reactive gases with inert carrier gas  in order to investigate their feasibility for use as post-implant encapsulants and/or device passivation layers for GaAs. The films and substrates are analyzed by ion channeling, ellipsometry, IR spectrometry, ESR, RBS, and SEM to evaluate implantationinduced substrate and interface damage as well as the films’ optical properties, surface morphology, stoichiometry, uniformity, stress, and electrical trapping characteristics. Following furnace or RTA annealing they are recharacterized, adding SIMS to evaluate As diffusion into the films. Both Schottky and ohmic contacts are then formed and used to measure Hall mobility, trap density and 1/f noise. Preliminary results of these studies are presented and compared with those obtained using other techniques such as wafer-to-wafer As entrapment, arsine overpressure, or conventional CVD.