The electrical properties of the Si-SiO2 interface following nitridation by ammonia plasma exposure at room temperature indicate that a high density of interface defects and charges is generated by the plasma exposure. Combined high-frequency and quasistatic capacitance-voltage measurements show a dramatic increase in the midgap defect density and interface charge, while quasi-steady-state photoconductivity decay measurements indicate a large increase in carrier recombination at the surfaces, as measured by an increase in the emitter saturation current density. The majority of the defects are not paramagnetic and are annealed out by a thermal treatment at 400 degrees C. However, some defects are also generated by the ammonia plasma exposure which is not removed by subsequent thermal treatments. A combination of ammonia plasma treatment and a subsequent 400 degrees C anneal results in good interface passivation, despite the generation of additional paramagnetic defects, making oxynitride layers produced in this way attractive for potential photovoltaic applications. (c) 2007 The Electrochemical Society.